Bony content of oxalate in patients with primary hyperoxaluria or oxalosis-unrelated renal failure

Prospective Assessment of the Prevalence of Enter Hyperoxalosis in Kidney Transplant Candidates

Enteric hyperoxalosis (EH) is an emerging cause of kidney transplantation (KT) dysfunction. We sought to determine the prevalence of EH and factors that affect plasma oxalate (POx) among at-risk KT candidates.

Methods

We prospectively measured POx among KT candidates evaluated at our center from 2017 to 2020 with risk factors for EH namely bariatric surgery, inflammatory bowel disease, or cystic fibrosis. EH was defined by a POx ≥10 μmol/L. Period-prevalence of EH was calculated. We compared mean POx across 5 factors: underlying condition, chronic kidney disease (CKD) stage, dialysis modality, phosphate binder type, and body mass index.

Results

Of 40 KT candidates screened, 23 had EH for a 4-y period prevalence of 58%. Mean POx was 21.6 ± 23.5 μmol/L ranging from 0 to 109.6 μmol/L. 40% of screened had POx >20 μmol/L. Sleeve gastrectomy was the most common underlying condition associated with EH. Mean POx did not differ by underlying condition (P = 0.27), CKD stage (P = 0.17), dialysis modality (P = 0.68), phosphate binder (P = 0.58), and body mass index (P = 0.56).

Conclusions

Bariatric surgery and inflammatory bowel disease were associated with a high prevalence of EH among KT candidates. Contrary to prior studies, sleeve gastrectomy was also associated with hyperoxalosis in advanced CKD. POx concentrations observed in EH reached levels associated with tissue and potentially allograft deposition. Concentrations can be as high as that seen in primary hyperoxaluria. More studies are needed to assess if POx is indeed a modifiable factor affecting allograft function in patients with EH.

Clinical practice recommendations for primary hyperoxaluria: an expert consensus statement from ERKNet and OxalEurope

Primary hyperoxaluria (PH) is an inherited disorder that results from the overproduction of endogenous oxalate, leading to recurrent kidney stones, nephrocalcinosis and eventually kidney failure; the subsequent storage of oxalate can cause life-threatening systemic disease. Diagnosis of PH is often delayed or missed owing to its rarity, variable clinical expression and other diagnostic challenges. Management of patients with PH and kidney failure is also extremely challenging. However, in the past few years, several new developments, including new outcome data from patients with infantile oxalosis, from transplanted patients with type 1 PH (PH1) and from patients with the rarer PH types 2 and 3, have emerged. In addition, two promising therapies based on RNA interference have been introduced. These developments warrant an update of existing guidelines on PH, based on new evidence and on a broad consensus. In response to this need, a consensus development core group, comprising (paediatric) nephrologists, (paediatric) urologists, biochemists and geneticists from OxalEurope and the European Rare Kidney Disease Reference Network (ERKNet), formulated and graded statements relating to the management of PH on the basis of existing evidence. Consensus was reached following review of the recommendations by representatives of OxalEurope, ESPN, ERKNet and ERA, resulting in 48 practical statements relating to the diagnosis and management of PH, including consideration of conventional therapy (conservative therapy, dialysis and transplantation), new therapies and recommendations for patient follow-up.

Chronic liver disease and hepatic calcium-oxalate deposition in patients with primary hyperoxaluria type I

Patients with primary hyperoxaluria type I (PH I) are prone to develop early kidney failure. Systemic deposition of calcium-oxalate (CaOx) crystals starts, when renal function declines and plasma oxalate increases. All tissue, but especially bone, heart and eyes are affected. However, liver involvement, as CaOx deposition or chronic hepatitis/fibrosis has never been reported. We examined liver specimen from 19 PH I patients (aged 1.5 to 52 years at sample collection), obtained by diagnostic biopsy (1), at autopsy (1), or transplantation (17). With polarization microscopy, birefringent CaOx crystals located in small arteries, but not within hepatocytes were found in 3/19 patients. Cirrhosis was seen in one, fibrosis in 10/19 patients, with porto-portal and nodular fibrosis (n = 1), with limitation to the portal field in 8 and/or to central areas in 5 patients. Unspecific hepatitis features were observed in 7 patients. Fiber proliferations were detectable in 10 cases and in one sample transformed Ito-cells (myofibroblasts) were found. Iron deposition, but also megakaryocytes as sign of extramedullary erythropoiesis were found in 9, or 3 patients, respectively. Overall, liver involvement in patients with PH I was more pronounced, as previously described. However, CaOx deposition was negligible in liver, although the oxalate concentration there must be highest.

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.

Vitamin C overload may contribute to systemic oxalosis in children receiving dialysis

BACKGROUND

Malnutrition and anorexia are common in children with chronic kidney disease (CKD) and gastrostomy tubes (GT) as well as nasogastric tubes (NGT) have been recommended to maximize nutritional support. The optimal requirement of vitamin C in children with CKD remains to be defined but oxalate is a breakdown product of vitamin C. Elevated vitamin C intake and bone oxalate were identified in two formula-fed dialyzed children with negative genetic testing for primary hyperoxaluria.

METHODS

We evaluated the impact of nutritional support on serum ascorbic acid and plasma oxalate levels in 13 dialyzed infants and young children.

RESULTS

All patients were fed by GT or NGT since the first months of life; overall patients were receiving between 145 and 847% of the age-specific DRI for vitamin C. Mean serum ascorbic acid and plasma oxalate levels were elevated (244.7 ± 139.7 μM/L and 44.3 ± 23.1 μM/L, respectively), and values did not differ according to the degree of residual kidney function. Ascorbic acid levels did not correlate with oxalate levels (r = 0.44, p = 0.13).

CONCLUSIONS

Excessive vitamin C intake may contribute to oxalate accumulation in dialyzed children.

The Struggling Odyssey of Infantile Primary Hyperoxaluria

Introduction: Oxalate overproduction in Primary Hyperoxaluria type I (PH1) leads to progressive renal failure and systemic oxalate deposition. In severe infantile forms of PH1 (IPH1), end-stage renal disease (ESRD) occurs in the first years of life. Usually, the management of these infantile forms is challenging and consists in an intensive dialysis regimen followed by a liver-kidney transplantation (combined or sequential). Methods: Medical records of all infants with IPH1 reaching ESRD within the first year of life, diagnosed and followed between 2005 and 2018 in two pediatric nephrology departments in Brussels and Paris, have been reviewed. Results: Seven patients were included. They reached ESRD at a median age of 3.5 (2-7) months. Dialysis was started at a median age of 4 (2-10 months). Peritoneal dialysis (PD) was the initial treatment for 6 patients and hemodialysis (HD) for one patient. Liver transplantation (LT) was performed in all patients and kidney transplantation (KT) in six of them. A sequential strategy has been chosen in 5 patients, a combined in one. The kidney transplanted as part of the combined strategy was lost. Median age at LT and KT was 25 (10-41) months and 32.5 (26-75) months, respectively. No death occurred in the series. At the end of a median follow-up of 3 years, mean eGFR was 64 ± 29 ml/min/1.73 m². All patients presented retinal and bone lesions and five patients presented bones fractures. Conclusion: Despite encouraging survival figures, the morbidity in IPH1 patients remains extremely heavy and its management presents a huge challenge. Thanks to the newly developed RNA-interference drug, the future holds brighter prospects.

Transplantation for Primary Hyperoxaluria Type 1: Designing New Strategies in the Era of Promising Therapeutic Perspectives

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disease caused by the functional defect of alanine-glyoxylate aminotransferase that results in the overproduction of oxalate. It can be devastating especially for kidneys, leading to end-stage renal disease (ESRD) during the first 2 to 3 decades of life in most patients. Consequently, many PH1 patients need kidney transplantation. However, because PH1 is caused by a liver enzyme deficiency, the only cure of the metabolic defect is liver transplantation. Thus, current transplant strategies to treat PH1 patients with ESRD include dual liver-kidney transplantation. However, the morbidity and mortality associated with liver transplantation make these strategies far from optimal. Fortunately, a therapeutic revolution is looming. Indeed, innovative drugs are being currently tested in clinical trials, and preliminary data show impressive efficacy to reduce the hepatic overproduction of oxalate. Hopefully, with these therapies, liver transplantation will no longer be necessary. However, some patients with progressing renal disease or those who will be diagnosed with PH1 at an advanced stage of chronic kidney disease will ultimately need kidney transplantation. Here we review the current knowledge on this subject and discuss the future of kidney transplant management in PH1 patients in the era of novel therapies.

End Points for Clinical Trials in Primary Hyperoxaluria

Patients with primary hyperoxaluria experience kidney stones from a young age and can develop progressive oxalate nephropathy. Progression to kidney failure often develops over a number of years, and is associated with systemic oxalosis, intensive dialysis, and often combined kidney and liver transplantation. There are no therapies approved by the Food and Drug Association. Thus, the Kidney Health Initiative, in partnership with the Oxalosis and Hyperoxaluria Foundation, initiated a project to identify end points for clinical trials. A workgroup of physicians, scientists, patients with primary hyperoxaluria, industry, and United States regulators critically examined the published literature for clinical outcomes and potential surrogate end points that could be used to evaluate new treatments. Kidney stones, change in eGFR, urine oxalate, and plasma oxalate were the strongest candidate end points. Kidney stones affect how patients with primary hyperoxaluria feel and function, but standards for measurement and monitoring are lacking. Primary hyperoxaluria registry data suggest that eGFR decline in most patients is gradual, but can be unpredictable. Epidemiologic data show a strong relationship between urine oxalate and long-term kidney function loss. Urine oxalate is reasonably likely to predict clinical benefit, due to its causal role in stone formation and kidney damage in CKD stages 1-3a, and plasma oxalate is likely associated with risk of systemic oxalosis in CKD 3b-5. Change in slope of eGFR could be considered the equivalent of a clinically meaningful end point in support of traditional approval. A substantial change in urine oxalate as a surrogate end point could support traditional approval in patients with primary hyperoxaluria type 1 and CKD stages 1-3a. A substantial change in markedly elevated plasma oxalate could support accelerated approval in patients with primary hyperoxaluria and CKD stages 3b-5. Primary hyperoxaluria type 1 accounts for the preponderance of available data, thus heavily influences the conclusions. Addressing gaps in data will further facilitate testing of promising new treatments, accelerating improved outcomes for patients with primary hyperoxaluria.

ENDOCRINE MANIFESTATIONS OF PRIMARY HYPEROXALURIA

OBJECTIVE

Primary hyperoxaluria type 1 (PH1) is a rare metabolic disorder of oxalate overproduction. It is associated with urolithiasis and nephrocalcinosis, which progress to end-stage renal disease and systemic oxalosis. As oxalate deposits in tissues, non-parathyroid hormone (nonPTH)-mediated hypercalcemia, oxalate osteopathy, primary hypothyroidism, and primary hypogonadism develop. In this review, we will present a case of PH1 and provide an overview of this clinical entity and its endocrine manifestations.

METHODS

We conducted a PubMed search for articles related to PH1. The terms "primary hyperoxaluria," "nonPTH mediated hypercalcemia," "hypothyroidism," and "hypogonadism" were used to identify pertinent literature.

RESULTS

Given the rarity of PH1, there is scant literature regarding the incidence and clinical significance of endocrine manifestations of this disorder. There are rare reports of hypercalcemia secondary to osteoclast-stimulating activity of macrophages in bone granulomas, which occur in response to oxalate deposits. We report that hypercalcemia may also be mediated by 1,25-dihydroxyvitamin D and PTH-related protein (PTHrP). Primary hypothyroidism and primary hypogonadism are thought to be due partly to calcium oxalate deposition in thyroid and testicular tissue. The presented case is the first to report PTHrP-mediated hypercalcemia and primary hypogonadism in a patient with PH1.

CONCLUSION

PH1 is a metabolic disease with significant morbidity and mortality. Owing to its rarity, it is not widely recognized in the field of endocrinology, despite presenting with several endocrinopathies. Recognition of endocrine disturbances can result in early and successful treatment, limiting morbidity and improving quality of life in these challenging patients.

ABBREVIATIONS

1,25(OH)₂D= 1,25-dihydoxyvitamin D AGT = alanine:glyoxylate aminotransferase ESRD = end-stage renal disease GRHPR = glyoxylate reductase-hydroxypyruvate reductase nonPTH = non-parathyroid hormone PH = primary hyperoxaluria pQCT = peripheral quantitative computed tomography PTH = parathyroid hormone PTHrP = parathyroid hormone-related protein T4 = thyroxine TSH = thyroid-stimulating hormone.

Type 1 primary hyperoxaluria: A case report and focus on bone impairment of systemic oxalosis

Primary hyperoxaluria is a rare genetic disorder characterized by oxalate overproduction, leading to kidney failure due to nephrocalcinosis, and is eventually responsible for systemic oxalosis. Bone impairment, secondary to oxalate deposits, is one of the many complications that may occur. Skeletal involvement can be difficult to diagnose because of lack of clinical symptoms and therefore needs to be confirmed by invasive testing, such as transiliac bone biopsy. If confirmed, bone oxalosis is the proof of disease severity and that combined liver-kidney transplantation should be performed.

Bone impairment in primary hyperoxaluria: a review

Deposition of calcium oxalate crystals in the kidney and bone is a hallmark of primary hyperoxaluria (PH). Since the bone compartment can store massive amounts of oxalate, patients present with recurrent low-trauma fractures, bone deformations, severe bone pains, and specific oxalate osteopathy on X-ray. Bone biopsy from the iliac crest displays specific features such as oxalate crystals surrounded by a granulomatous reaction corresponding to an invasion of bone surface by macrophages. The objective of this manuscript is therefore to provide an overview of bone impairment in PH, by reviewing the current literature on bone and dental symptoms as well as imaging techniques used for assessing bone disease.

Acute oxalate nephropathy following kidney transplantation: Report of three cases

Calcium oxalate (CaOx) crystal deposition is a common finding immediately after kidney transplantation. However, small depositions of CaOx could be benign while extensive depositions lead to poor graft outcome. Here we report three cases with end-stage renal disease (ESRD), bilateral nephrolithiasis, and unknown diagnosis of primary hyperoxaluria (PH) who underwent a renal transplant and experienced an early-onset graft failure. Although an acute rejection was suspected, renal allograft biopsies and subsequent allograft nephrectomies showed extensive CaOx deposition, which raised a suspicion of PH. Even though increased urinary excretion of CaOx was found in all patients, this diagnosis could be confirmed with further tests including genetic study and metabolic assay. In conclusion, massive CaOx deposition in kidney allograft is an important cause of poor allograft survival and needs special management. Furthermore, our cases suggest patients with ESRD and a history of nephrolithiasis should be screened for elevated urinary oxalate excretion and rule out of PH.

Bone impairment in oxalosis: An ultrastructural bone analysis

Deposition of calcium oxalate crystals in the kidney and bone is a hallmark of systemic oxalosis. Since the bone compartment can store massive amounts of oxalate, patients present with recurrent low-trauma fractures, bone deformations, severe bone pains and specific oxalate osteopathy on plain X-ray. Bone biopsy from the iliac crest displays specific features such as oxalate crystals surrounded by a granulomatous reaction due to an invasion of bone surface by macrophages. We present data obtained in 10 samples from 8 patients with oxalosis (16-68 years) who underwent iliac crest bone biopsy and bone quality analysis using modern methods (microradiography, microindentation, Fourier Transform InfraRed Microspectroscopy, transmission electron microscopy) in addition to histomorphometry. Disseminated calcium oxalate deposits (whewellite) were found in the bone marrow space (with a granulomatous reaction) but not in the bone matrix. Calcium oxalate deposits were totally surrounded by macrophages and multinucleated giant cells, and a phagocytosis activity was sometimes observed. Very few calcium oxalate crystals were directly in close contact with the mineral substance of the bone. Bone mineralization was not modified by the presence of calcium oxalate even in close vicinity. Bone quality analysis also revealed a harder bone than normal, perhaps in relationship with decreased carbonate content in the mineral. This increase in bone hardness could explain a more "brittle" bone. In patients with oxalosis, the formation and growth of calcium oxalate crystals in the bone appeared independent of apatite. The mechanisms leading to nucleation and growth of oxalate deposits are still unclear and deserve further studies.

Oxalate quantification in hemodialysate to assess dialysis adequacy for primary hyperoxaluria

BACKGROUND

Patients with primary hyperoxaluria (PH) overproduce oxalate which is eliminated via the kidneys. If end-stage kidney disease develops they are at high risk for systemic oxalosis, unless adequate oxalate is removed during hemodialysis (HD) to equal or exceed ongoing oxalate production. The purpose of this study was to validate a method to measure oxalate removal in this unique group of dialysis patients.

METHODS

Fourteen stable patients with a confirmed diagnosis of PH on HD were included in the study. Oxalate was measured serially in hemodialysate and plasma samples in order to calculate rates of oxalate removal. HD regimens were adjusted according to a given patient's historical oxalate production, amount of oxalate removal at dialysis, residual renal clearance of oxalate, and plasma oxalate levels.

RESULTS

After a typical session of HD, plasma oxalate was reduced by 78.4 ± 7.7%. Eight patients performed HD 6 times/week, 2 patients 5 times/week, and 3 patients 3 times/week. Combined oxalate removal by HD and the kidneys was sufficient to match or exceed endogenous oxalate production. After a median period of 9 months, pre-dialysis plasma oxalate was significantly lower than initially (75.1 ± 33.4 vs. 54.8 ± 46.6 mmol/l, p = 0.02).

CONCLUSION

This methodology can be used to individualize the dialysis prescription of PH patients to prevent oxalosis during the time they are maintained on HD and to reduce risk of oxalate injury to a transplanted kidney.

The colon: an overlooked site for therapeutics in dialysis patients

Morbidity and mortality related to chronic kidney disease remain unacceptably high, despite tremendous progress in its prevention and treatment. In an ongoing quest to improve outcome in chronic kidney disease patients, the colon might be an appealing, but largely underexplored, therapeutic target. A clear bi-directional functional relationship exists between the colon and kidney, also referred as to the colo-renal axis. Uremia has an important impact on the colonic microbiome. The microbiome, in turn, is an important source of uremic toxins, with p-cresyl sulfate and indoxyl sulfate as important prototypes. These co-metabolites accumulate in the face of a falling kidney function, and may accelerate the progression of renal and cardiovascular disease. Several therapeutic interventions, including prebiotics and adsorbants, specifically target these colon-derived uremic toxins originating from bacterial metabolism. As kidney function declines, the colon also gains importance in the homeostasis and disposal of potassium and oxalate. Their colonic secretion may be increased by drugs increasing the expression of cAMP and by probiotics (e.g., Oxalobacter formigenes).

Hyperoxaluria and systemic oxalosis: an update on current therapy and future directions

INTRODUCTION

The primary hyperoxalurias (PH) are rare, but underdiagnosed disorders where the loss of enzymatic activity in key compounds of glyoxylate metabolism results in excessive endogenous oxalate generation. Clinically, they are characterized by recurrent urolithiasis and/or nephrocalcinosis. PH type I is the most frequent and most devastating subtype often leading to early end-stage renal failure.

AREAS COVERED

Profound overview of clinical, diagnostic, and currently available treatment options with a focus on PH I at different stages of the disease. Discussion of future therapeutic avenues including pharmacological chaperones (small molecules rescuing protein function), gene therapy with safer adenoviral vectors, and potential application of cell-based transplantation strategies is provided.

EXPERT OPINION

Due to lack of familiarity with PH and its heterogeneous clinical expression, diagnosis is often delayed until advanced disease is present, a condition, requiring intensive hemodialysis and timely transplantation. Achieving the most beneficial outcome largely depends on the knowledge of the clinical spectrum, early diagnosis, and initiation of treatment before renal failure ensues. A number of preconditions required for substantial improvement in the care of orphan disease like PH have now been achieved or soon will come within reach, so new treatment options can be expected in the near future.

Primary hyperoxaluria

Primary hyperoxalurias (PH) are inborn errors in the metabolism of glyoxylate and oxalate. PH type 1, the most common form, is an autosomal recessive disorder caused by a deficiency of the liver-specific enzyme alanine, glyoxylate aminotransferase (AGT) resulting in overproduction and excessive urinary excretion of oxalate. Recurrent urolithiasis and nephrocalcinosis are the hallmarks of the disease. As glomerular filtration rate decreases due to progressive renal damage, oxalate accumulates leading to systemic oxalosis. Diagnosis is often delayed and is based on clinical and sonographic findings, urinary oxalate assessment, DNA analysis, and, if necessary, direct AGT activity measurement in liver biopsy tissue. Early initiation of conservative treatment, including high fluid intake, inhibitors of calcium oxalate crystallization, and pyridoxine in responsive cases, can help to maintain renal function in compliant subjects. In end-stage renal disease patients, the best outcomes have been achieved with combined liver-kidney transplantation which corrects the enzyme defect.

[Primary hyperoxaluria]

Primary hyperoxalurias are rare recessive inherited inborn errors of glyoxylate metabolism. They are responsible for progressive renal involvement, which further lead to systemic oxalate deposition, which can even occur in infants. Primary hyperoxaluria type 1 is the most common form in Europe and is due to alanine-glyoxylate aminostransferase deficiency, a hepatic peroxisomal pyridoxin-dependent enzyme. Therefore primary hyperoxaluria type 1 is responsible for hyperoxaluria leading to aggressive stone formation and nephrocalcinosis. As glomerular filtration rate decreases, systemic oxalate storage occurs throughout all the body, and mainly in the skeleton. The diagnosis is first based on urine oxalate measurement, then on genotyping, which may also allow prenatal diagnosis to be proposed. Conservative measures - including hydration, crystallization inhibitors and pyridoxine - are safe and may allow long lasting renal survival, provided it is given as soon as the diagnosis has been even suspected. No dialysis procedure can remove enough oxalate to compensate oxalate overproduction from the sick liver, therefore a combined liver and kidney transplantation should be planned before advanced renal disease has occurred, in order to limit/avoid systemic oxalate deposition. In the future, primary hyperoxaluria type 1 may benefit from hepatocyte transplantation, chaperone molecules, etc.

Bone metabolism in oxalosis: a single-center study using new imaging techniques and biomarkers

The deposition of calcium oxalate crystals in the kidney and bone is a hallmark of primary hyperoxaluria type 1 (PH1). We report here an evaluation of the bone status of 12 PH1 children based on bone biomarkers [parathyroid hormone, vitamin D, fibroblast growth factor 23 (FGF23)] and radiological assessments (skeletal age, three-dimensional high-resolution peripheral quantitative computed tomography, HR-pQCT) carried out within the framework of a cross-sectional single-center study. The controls consisted of healthy and children with chronic kidney disease already enrolled in local bone and mineral metabolism studies. The mean age (+ or - standard deviation) age of the patients was 99 (+ or - 63) months. Six children suffered from fracture. Bone maturation was accelerated in five patients, four of whom were <5 years. The combination of new imaging techniques and biomarkers highlighted new and unexplained features of PH1: advanced skeletal age in young PH1 patients, increased FGF23 levels and decreased total volumetric bone mineral density with bone microarchitecture alteration.

Parenteral ascorbic acid in haemodialysis patients

PURPOSE OF REVIEW

Parenteral ascorbic acid has been frequently used to overcome problems of vitamin C deficiency in haemodialysis patients. The benefits of vitamin C supplementation in clinical studies have been controversial and did not consider toxicological aspects. The review summarizes recent findings of the effects of parenteral ascorbic acid and discusses toxicological effects.

RECENT FINDINGS

Vitamin C deficiency in haemodialysis patients, which has been frequently described, cannot be improved with oral supplementation due to limited absorption of high dosages. To avoid consequences of vitamin C deficiency, parenteral vitamin C solutions should be administered because this intervention is the only way to guarantee a sufficient supply to the cells. A beneficial consequence of parenteral vitamin C on the recombinant human erythropoietin resistance is an additional therapeutic effect, which contributes to the prevention of iron deficiency anaemia in haemodialysis patients. Thus, large amount of supplemental vitamin C are required for extended periods of time (up to 500 mg 3 times a week). To avoid hyperoxaluria, plasma oxalate levels should be monitored on a regular basis, for example, once a week.

SUMMARY

Parenteral administration of ascorbic acid may be an approach that can overcome problems of vitamin C deficiency in haemodialysis patients - in particular problems of iron overload, erythropoetin resistance, and chronic inflammation.

[Inherited monogenic kidney stone diseases: recent diagnostic and therapeutic advances]

Hereditary monogenic kidney stone diseases are rare diseases, since they account for nearly 2% of nephrolithiasis cases in adults and 10% in children. Most of them are severe, because they frequently are associated with nephrocalcinosis and lead to progressive impairment of renal function unless an early and appropriate etiologic treatment is instituted. Unfortunately, treatment is often lacking or started too late since they are often misdiagnosed or overlooked. The present review reports the genotypic and phenotypic characteristics of monogenic nephrolithiases, with special emphasis on the recent advances in the field of diagnosis and therapeutics. Monogenic stone diseases will be classified into three groups according to their mechanism: (1) inborn errors of the metabolism of oxalate (primary hyperoxalurias), uric acid (hereditary hyperuricemias) or other purines (2,8-dihydroxyadeninuria), which, in addition to stone formation, result in crystal deposition in the renal parenchyma; (2) congenital tubulopathies affecting the convoluted proximal tubule (such as Dent's disease, Lowe syndrome or hypophosphatemic rickets), the thick ascending limb of Henlé's loop (such as familial hypomagnesemia and Bartter's syndromes) or the distal past of the nephron (congenital distal tubular acidosis with or without hearing loss), which are frequently associated with nephrocalcinosis, phosphatic stones and extensive tubulointerstitial fibrosis; (3) cystinuria, an isolated defect in tubular reabsorption of cystine and dibasic aminoacids, which results only in the formation of stones but requires a cumbersome treatment. Analysis of stones appears of crucial value for the early diagnosis of these diseases, as in several of them the morphology and composition of stones is specific. In other cases, especially if nephrocalcinosis, phosphatic stones or proteinuria are present, the evaluation of blood and urine chemistry, especially with regard to calcium, phosphate and magnesium, is the key of diagnosis. Search for mutations is now increasingly performed in as much as genetic counselling is important for the detection of heterozygotes in autosomic recessive diseases and of carrier women in X-linked diseases. In conclusion, better awareness to the rare monogenic forms of nephrolithiasis and/or nephrocalcinosis should allow early diagnosis and treatment which are needed to prevent or substantially delay progression of end-stage renal disease. Analysis of every first stone both in children and in adults should never be neglected, in order to early detect unusual forms of nephrolithiasis requiring laboratory evaluation and deep etiologic treatment.

Body growth after combined liver-kidney transplantation in children with primary hyperoxaluria type 1

BACKGROUND

Children with primary hyperoxaluria type 1 (PH1) often develop severe growth failure, which is related to metabolic and endocrine consequences of chronic renal failure, and/or oxalate deposition in bone and cartilage. Combined liver and kidney transplantation (LKT) corrects the underlying metabolic defect and restores renal function in these children.

METHODS

We therefore analyzed longitudinal growth of 24 children with PH1 who underwent LKT at nine European centers. Mean age at LKT was 8.9 years, and mean duration of follow-up was 5.7 years.

RESULTS

After LKT mean standardized height tended to increase from -1.79 SD to -1.47 SD until last observation. Mean adult height amounted to 167 cm and 158 cm in boys and girls, respectively. At last observation, seven out of 24 patients were stunted. Within the whole study population, the degree of catch-up growth after LKT was positively associated with degree of stunting at the time of LKT and negatively associated with prednisolone dosage explaining together 39% of the overall variability.

CONCLUSIONS

Combined LKT does not induce true catch-up growth in the majority of children with PH1. Due to the preexisting growth retardation at the time of LKT, one third of patients end up with a reduced final height.

Primary hyperoxaluria type 1: still challenging!

Primary hyperoxaluria type 1, the most common form of primary hyperoxaluria, is an autosomal recessive disorder caused by a deficiency of the liver-specific enzyme alanine: glyoxylate aminotransferase (AGT). This results in increased synthesis and subsequent urinary excretion of the metabolic end product oxalate and the deposition of insoluble calcium oxalate in the kidney and urinary tract. As glomerular filtration rate (GFR) decreases due to progressive renal involvement, oxalate accumulates and results in systemic oxalosis. Diagnosis is still often delayed. It may be established on the basis of clinical and sonographic findings, urinary oxalate +/- glycolate assessment, DNA analysis and, sometimes, direct AGT activity measurement in liver biopsy tissue. The initiation of conservative measures, based on hydration, citrate and/or phosphate, and pyridoxine, in responsive cases at an early stage to minimize oxalate crystal formation will help to maintain renal function in compliant subjects. Patients with established urolithiasis may benefit from extracorporeal shock-wave lithotripsy and/or JJ stent insertion. Correction of the enzyme defect by liver transplantation should be planned, before systemic oxalosis develops, to optimize outcomes and may be either sequential (biochemical benefit) or simultaneous (immunological benefit) liver-kidney transplantation, depending on facilities and access to cadaveric or living donors. Aggressive dialysis therapies are required to avoid progressive oxalate deposition in established end-stage renal disease (ESRD), and minimization of the time on dialysis will improve both the patient's quality of life and survival.

Long-term, low-dose, intravenous vitamin C leads to plasma calcium oxalate supersaturation in hemodialysis patients

BACKGROUND

Ascorbate supplementation for patients on regular dialysis treatment (RDT) is advised to obviate deficiency and improve epoetin response in those with functional iron deficiency. However, clear-cut safety concerns regarding hyperoxalemia are still poorly understood. This study tries to establish safety/efficacy profiles of ascorbate and oxalate during long-term intravenous ascorbate supplementation.

METHODS

A prospective study was performed in 30 patients on RDT showing ascorbate deficiency (plasma ascorbate < 2.6 mg/L [<15 micromol/L]): 18 patients were administered intravenous ascorbate during 18 months (250 mg/wk, subsequently increased to 500 mg), and 12 patients were taken as reference untreated cases. Plasma ascorbate and oxalate assays and dialytic balance determinations were performed (ion chromatography and reverse-phase high-performance liquid chromatography, respectively) at baseline, during treatment, and 12 months after withdrawal.

RESULTS

Plasma ascorbate levels increased dose dependently with supplementation (1.6 +/- 0.8 mg/L [9.1 +/- 4.6 mumol/L] at baseline, 2.8 +/- 1.8 mg/L [15.9 +/- 10.1 micromol/L]) with 250 mg of ascorbate, and 6.6 +/- 2.8 mg/L [37.5 +/- 16.0 micromol/L] with 500 mg/wk of ascorbate), but only normalized with greater dosages for several months in 94% of patients. Baseline plasma oxalate levels increased from 3.2 +/- 0.8 mg/L (35.8 +/- 8.8 micromol/L) to 3.6 +/- 0.8 mg/L (39.5 +/- 9.1 micromol/L) and 4.5 +/- 0.9 mg/L (50.3 +/- 10.4 micromol/L) with 250 and 500 mg, respectively ( P < 0.001). The calcium oxalate saturation threshold was exceeded by 7 of 18 patients (40%) during 6 months therapy with 500 mg/wk. Ascorbate dialysis removal increased from 37.8 +/- 23.2 mg (215 +/- 132 micromol) to 99.6 +/- 51.7 mg (566 +/- 294 micromol) during supplementation (P < 0.001), with corresponding increases in oxalate removal from 82.5 +/- 33.2 mg (917 +/- 369 micromol) to 111.2 +/- 32.6 mg/L (1,236 +/- 362 micromol; P < 0.01). Withdrawal reverted plasma levels and dialysis removal to initial values. Values for untreated patients did not change during 1 year of follow-up.

CONCLUSION

Patients on RDT may resolve ascorbate deficiency with intravenous supplementation of 500 mg/wk, but this implies a significant risk for oxalate supersaturation. Oxalate measurements are strongly recommended during long-term ascorbate therapy.

Severe course of primary hyperoxaluria and renal failure after domino hepatic transplantation

We report herein a domino orthotopic liver transplantation (LT), from a 38-year-old woman undergoing liver-kidney transplantation (LKT) for primary hyperoxaluria type I (PH1) to a recipient with cirrhosis and hepatocellular carcinoma. Delayed onset of PH1 and renal failure and 10% residual alanine-glyoxylate aminotransferase (AGT) activity in domino liver justified its use for domino procedure. The clinical course after LKT was similar to that described in other series, including ours. Renal function started promptly and maintained despite sustained hyperoxaluria from dissolution of oxalotic deposits. Conversely, the domino recipient manifested severe hyperoxaluria and developed nephrolithiasis and renal insufficiency with rapid progression over 2 months. A new LT resulted in slow decrease of oxaluria and improvement of renal function. Therefore, PH1 behaved quite differently in these two patients, leading us to conclude that domino LT using livers from PH1 patients should be considered very carefully, only as a bridge to definitive LT in recipients with critical clinical conditions.

Low water-soluble uremic toxins

The uremic syndrome is the result of the retention of solutes, which under normal conditions are cleared by the healthy kidneys. Uremic retention products are arbitrarily subdivided according to their molecular weight. Low-molecular-weight molecules are characterized by a molecular weight below 500 D. The purpose of the present publication is to review the main water soluble, nonprotein bound uremic retention solutes, together with their main toxic effects. We will consecutively discuss creatinine, glomerulopressin, the guanidines, the methylamines, myo-inositol, oxalate, phenylacetyl-glutamine, phosphate, the polyamines, pseudouridine, the purines, the trihalomethanes, and urea per se.

Bone mineral density in children with primary hyperoxaluria type I

BACKGROUND

In primary hyperoxaluria type I (PH 1), hepatic overproduction of oxalate leads to its deposition in various organ systems including bone (oxalosis). To evaluate skeletal status non-invasively in PH 1 we measured bone mineral density (BMD).

METHODS

Peripheral quantitative computed tomography of the distal radius was performed in 10 children with PH 1 (mean chronological age 9+/-3.1, mean skeletal age 8.3+/-3.0 years): seven were on conservative treatment (CT) including one patient after pre-emptive liver transplantation (PH1-CT) and three were studied with end-stage renal disease on peritoneal dialysis (PH1-ESRD).

RESULTS

Mean trabecular bone density (TBD) was significantly increased in PH1-ESRD compared with both age-matched healthy and uraemic controls (65227 vs. 168+/-63 and 256+/-80 mg/cm(3); P<0.002 and P<0.007, respectively), while cortical bone density (CBD) was elevated to a lesser degree (517+/-23 vs. 348+/-81 vs. 385+/-113 mg/cm(3); P<0.02 and P<0.04, respectively). In PH 1, CBD and, even more so, TBD were significantly correlated with serum creatinine (r=0.91 and r=0.96, P<0.0001, respectively) and plasma oxalate levels (r=0.86 and r=0.94, P<0.001 and P<0.0001, respectively). In children with PH 1 and normal glomerular function, both CBD and TBD were comparable with healthy controls.

CONCLUSION

These preliminary data suggest that in PH 1 BMD is significantly increased in ESRD, probably due to oxalate disposal. Measurement of BMD may be a valuable and non-invasive tool in determining and monitoring oxalate burden in this disorder.

Plasma calcium oxalate supersaturation in children with primary hyperoxaluria and end-stage renal failure

BACKGROUND

Children with primary hyperoxaluria type 1 (PH 1) are at great risk to develop systemic oxalosis in end-stage renal disease (ESRD), as endogenous oxalate production exceeds oxalate removal by dialytic therapy. As oxalate accumulates, calcium oxalate (CaOx) tissue deposition occurs. Children with other causes of ESRD, however, are not prone to CaOx deposition despite elevated plasma oxalate (POx) levels.

METHODS

Our study objective was to examine the potential mechanisms for these observations. We measured POx, sulfate, citrate, and calculated CaOx saturation (betaCaOx) in 7 children with ESRD caused by PH 1 and in 33 children with non-PH-related ESRD. Maintenance hemodialysis (HD) was performed in 6 PH 1 and 22 non-PH patients: Pre- and post-HD levels were analyzed at this point and were repeated twice within 12 months in 5 PH 1 and 14 non-PH patients. Samples were obtained only once in 12 patients (one PH 1) on peritoneal dialysis (PD). After liver-kidney or kidney transplantation, plasma levels were measured repetitively.

RESULTS

The mean POx was higher in PH 1 (125.7 +/- 17.9 micromol/liter) than in non-PH patients (44.2 +/- 3.3 micromol/liter, P < 10(-4)). All other determined anions did not differ between the two groups. betaCaOx was higher in PH 1 (4.71 +/- 0.69 relative units) compared with non-PH children (1.56 +/- 0.12 units, P < 10(-4)). POx and betaCaOx were correlated in both the PH 1 (r = 0.98, P < 2 x 10(-4)) and the non-PH group (r = 0.98, P < 10(-4)). POx and betaCaOx remained stable over time in the non-PH children, whereas an insignificant decline was observed in PH 1 patients after six months of more aggressive dialysis. betaCaOx was supersaturated (more than 1) in all PH 1 and in 25 out of 33 non-PH patients. Post-HD betaCaOx remained more than 1 in all PH 1, but in only 2 out of 22 non-PH patients. In non-PH children, POx and betaCaOx decreased to normal within three weeks after successful kidney transplantation, whereas the levels still remained elevated seven months after combined liver-kidney transplantation in two PH 1 patients.

CONCLUSION

Systemic oxalosis in PH 1 children with ESRD is due to higher POx and betaCaOx levels. As betaCaOx remained supersaturated in PH 1 even after aggressive HD, oxalate accumulation increases, and CaOx tissue deposition occurs. Therefore, sufficient reduction of POx and betaCaOx is crucial in PH 1 and might only be achieved by early, preemptive, combined liver-kidney transplantation or liver transplantation alone.