STUDIES ON PRIMARY HYPEROXALURIA. I. IN VIVO DEMONSTRATION OF A DEFECT IN GLYOXYLATE METABOLISM

Small Molecule-Based Enzyme Inhibitors in the Treatment of Primary Hyperoxalurias

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism. PHs classification based on gene mutations parallel a variety of enzymatic defects, and all involve the harmful accumulation of calcium oxalate crystals that produce systemic damage. These geographically widespread rare diseases have a deep impact in the life quality of the patients. Until recently, treatments were limited to palliative measures and kidney/liver transplants in the most severe forms. Efforts made to develop pharmacological treatments succeeded with the biotechnological agent lumasiran, a siRNA product against glycolate oxidase, which has become the first effective therapy to treat PH1. However, small molecule drugs have classically been preferred since they benefit from experience and have better pharmacological properties. The development of small molecule inhibitors designed against key enzymes of glyoxylate metabolism is on the focus of research. Enzyme inhibitors are successful and widely used in several diseases and their pharmacokinetic advantages are well known. In PHs, effective enzymatic targets have been determined and characterized for drug design and interesting inhibitory activities have been achieved both in vitro and in vivo. This review describes the most recent advances towards the development of small molecule enzyme inhibitors in the treatment of PHs, introducing the multi-target approach as a more effective and safe therapeutic option.

Contribution of Dietary Oxalate and Oxalate Precursors to Urinary Oxalate Excretion

Kidney stone disease is increasing in prevalence, and the most common stone composition is calcium oxalate. Dietary oxalate intake and endogenous production of oxalate are important in the pathophysiology of calcium oxalate stone disease. The impact of dietary oxalate intake on urinary oxalate excretion and kidney stone disease risk has been assessed through large cohort studies as well as smaller studies with dietary control. Net gastrointestinal oxalate absorption influences urinary oxalate excretion. Oxalate-degrading bacteria in the gut microbiome, especially Oxalobacter formigenes, may mitigate stone risk through reducing net oxalate absorption. Ascorbic acid (vitamin C) is the main dietary precursor for endogenous production of oxalate with several other compounds playing a lesser role. Renal handling of oxalate and, potentially, renal synthesis of oxalate may contribute to stone formation. In this review, we discuss dietary oxalate and precursors of oxalate, their pertinent physiology in humans, and what is known about their role in kidney stone disease.

Effects of fabrication parameters on viscoelastic shear modulus of 2,3-dialdehydecellulose membranes--potential scaffolds for vocal fold lamina propria tissue engineering

Porous 2,3-dialdehydecellulose (2,3-DAC) membranes were investigated for use as a synthetic scaffold for engineering vocal fold-like tissues. Two criteria of this application are (i) the viscoelastic shear properties of the scaffold should be controllable in the range of vocal fold tissues and (ii) scaffolds should remain biomechanically stable to withstand vibrational stresses in a bioreactor. Porous 2,3-DAC membranes were fabricated from methylolcellulose by water-induced cellulose regeneration, with or without sodium chloride leaching, followed by periodate oxidation. They were freeze-dried and ethylene oxide-sterilized. Different degrees of oxidation were obtained on reacting with sodium metaperiodate for different time points. Rheological studies were performed to investigate the effect of freeze-drying, porosity, degree of oxidation, sterilization, and incubation time on elastic and viscous shear moduli, G' and G'', respectively, for frequencies 0.01-10 Hz. Freeze drying increased G' and G'', while increased porosity and degree of oxidation reduced G' and G''. Sterilization had no effect on viscoelasticity. When incubated in Dulbecco's minimum essential medium at 37 degrees C, membranes with 6-7% and 19-20% oxidation disintegrated after 7 and 3 days, respectively, while membranes with 3-4% oxidation showed little viscoelastic change over a period of 42 days. The upper frequency limit of rheologic measurement was a limitation of the study and should be addressed in future investigations.

Fabrication and evaluation of porous 2,3-dialdehydecellulose membrane as a potential biodegradable tissue-engineering scaffold

A simple, novel method to produce porous 2,3-dialdehydecellulose (DAC) membranes as a potential tissue-engineering scaffold has been developed from methylolcellulose by the simultaneous water-induced phase separation and sodium chloride salt leaching techniques, followed by oxidation with sodium periodate in water. Membrane pores increased in size with increasing weight or particle size of the sodium chloride salt. The porosity of the membrane was not affected by the salt particle size, but it increased with an increase in the salt weight to 60%. At higher salt weight percentages, no significant change in the membrane porosity was observed. The oxidation step had no effect on the membrane porosity or pore size. All membranes with a porosity value ranging between 87 and 93% showed interconnected porous structures. The use of these membranes as a potential tissue-engineering scaffold was evaluated with the use of human neonatal skin fibroblast cells. Confocal microscopy showed cell attachment and spreading on these membranes. Immunohistochemical tests revealed the presence of collagen type III and fibronectin, indicating that the cells were viable and formed the extracellular matrix. In conclusion, the DAC membrane supports cell adhesion and proliferation and hence shows potential to be used as a tissue-engineering scaffold.

Renal calcium phosphate and oxalate deposition in prolonged vitamin B6 deficiency: studies on a rat model of urolithiasis

OBJECTIVE

To determine the effect on kidney oxalate-salt deposition of a prolonged diet which induced vitamin B6 deficiency in adult rats, as there are reports of the pathogenic involvement of vitamin B6 deficiency in the formation of renal calcium oxalate calculi.

MATERIALS AND METHODS

The study comprised 24 6-month-old male albino Wistar rats; 12 were fed with a purified vitamin B6-deficient diet and the others provided with the same diet but supplemented with 6 mg/kg of vitamin B6. After 12 weeks, all rats were killed, and their kidneys fixed in formalin and routinely processed to paraffin for morphological examination; some fragments were fixed in glutaraldehyde and prepared for ultrastructural examination. From each rat consecutive sections of both kidneys were cut and stained with haematoxylin and eosin, periodic-acid Schiff, Sirius red and the Von Kossa method for calcium. Sections were examined in polarized light and by electron microscopy.

RESULTS

The histopathological and ultrastructural features of the kidney of vitamin B6-deficient rats were those of tubular-interstitial nephritis, characterized by tubular atrophy, interstitial fibrosis and chronic inflammatory infiltration. Oxalate and phosphate crystals were present in the papillary and parenchymal connective tissue. Ultrastructural features confirmed severe tubular epithelial lesions and the presence of an interstitial and intraepithelial inflammatory infiltrate; there was mild interstitial fibrosis. None of these features were apparent in the kidney of control rats.

CONCLUSIONS

Histopathological and ultrastructural data indicate that a prolonged vitamin B6-deficient diet may contribute to the formation and deposition of calcium phosphate and oxalate crystals, which lead to severe damage of the renal parenchyma. This phenomenon may occur not only in growing rats, which have more active protein metabolism and consequently higher vitamin B6 requirements, but also in adult rats.

Results of long-term treatment with orthophosphate and pyridoxine in patients with primary hyperoxaluria

BACKGROUND

The prognosis for patients with primary hyperoxaluria has been ominous, with the expectation of renal failure, poor results with transplantation, and early death.

METHODS

We studied the long-term effects of orthophosphate and pyridoxine therapy in 25 patients with primary hyperoxaluria who were treated for an average of 10 years (range, 0.3 to 26). Their mean age at the start of treatment was 12 years (median, 6; range, 0.5 to 32). We also studied the effect of orthophosphate and pyridoxine on urinary supersaturation with calcium oxalate, crystal inhibition using a seeded growth system, and crystal formation using scanning electron microscopy in 12 patients during three-day stays in the clinical research center.

RESULTS

The mean (+/- SD) glomerular filtration rate at the start of treatment was 91 +/- 26 ml per minute per 1.73 m2. The median decline in glomerular filtration rates was 1.4 ml per minute per 1.73 m2 of body-surface area per year. The actuarial survival free of end-stage renal disease was 96, 89, 74, and 74 percent of 5, 10, 15, and 20 years, respectively. Treatment with orthophosphate and pyridoxine reduced urinary supersaturation with calcium oxalate from 8.3 +/- 3.0 to 2.1 +/- 1.7 kJ per mole at 38 degrees C (P < 0.001), increased the inhibition of calcium oxalate formation from 63 +/- 11 to 108 +/- 10 inhibitor units per 24 hours (P < 0.001), and improved the crystalluria score from 2.6 +/- 0.3 to 0.6 +/- 0.1 (P < 0.001).

CONCLUSIONS

Treatment of patients with primary hyperoxaluria with orthophosphate and pyridoxine decreases urinary calcium oxalate crystallization and appears to preserve renal function.

Ethylene Glycol Intoxication

Commonly available as automotive antifreeze, ethylene glycol can cause toxicity and death if ingested. It is metabolized to several aldehyde and acid intermediates that can cause severe metabolic acidosis, central nervous system derangements, cardiorespiratory failure, and acute renal failure. A presumptive diagnosis can often be made by assessment of the anion gap and the osmol gap and the finding of metabolic acidosis. Corroborating findings include oxalate crystalluria and urine that fluoresces on exposure to ultraviolet light. Recognition is important because there are specific treatment methods available. Therapy consists of administering sodium bicarbonate to counter the acidosis, ethanol to slow the generation of toxic metabolites, and vitamin cofactors, which may speed detoxification of these intermediates. Hemodialysis is employed to remove both ethylene glycol and its metabolites, to correct the acidbase disturbances, and as treatment for acute renal failure.

X-linked recessive nephrolithiasis with renal failure

BACKGROUND AND METHODS

Nephrolithiasis may occur as a consequence of a number of hereditary disorders. We describe a large kindred from northern New York with hereditary nephrolithiasis accompanied by urinary concentrating defects, nephrocalcinosis, renal insufficiency, and renal wasting of potassium, phosphate, calcium, and uric acid. The pattern of inheritance was established by examining the patients and their records and interviewing family members. Selected members of the family were evaluated in detail, with measurements of erythrocyte cation fluxes and carbonic anhydrase (carbonate dehydratase) activity.

RESULTS

The kindred consisted of 162 family members from six generations. All nine affected persons were male and appeared to have inherited the disease from their mothers. No affected man transmitted the gene to a son, but the daughters of affected men were carriers. The patients presented in childhood with calcium nephrolithiasis and proteinuria, with progression to nephrocalcinosis, urinary concentrating defects, and renal insufficiency. Renal biopsies revealed tubular atrophy, interstitial fibrosis, and glomerulosclerosis; the characteristic features of other forms of hereditary nephritis were absent. Abnormalities in the renal excretion of calcium, phosphate, potassium, and uric acid were found only in the adult members of the kindred, although renal biopsies were abnormal even in younger members. In one patient who has had a renal transplant for seven years, the disease has not recurred.

CONCLUSIONS

This kindred manifested an X-linked recessive nephrolithiasis with renal failure, a new form of hereditary renal disease. Most of the identifiable physiologic abnormalities occurred after the development of nephrolithiasis and renal insufficiency and may not be of pathogenetic importance.

[Type I oxalosis in childhood--studies within the scope of terminal renal failure in the child]

The difficulties of biochemical diagnosis in children and in chronic renal failure are discussed in detail, as well as the development of diagnostic and therapeutic possibilities in recent years, exemplified by 4 cases. Excretion of oxalate (and glycolate) may be incorrectly assumed to be normal with: a) uncritical application of the method of measurement, b) disregard of the clearly lower oxalate excretion in children (values should be referred to m2 of body surface), c) disregard of a decreased glomerular filtration rate (values should be referred to the creatinine clearance). With compromised renal function the excretion of oxalate and glycolate in primary oxalosis drops to "normal" whereas plasma values increase considerably. In this case the biochemical diagnosis is possible only by measurement of plasma values of glycolate and oxalate. Consequently, extensive extrarenal deposition of calcium oxalate crystals will, as a rule, become clinically manifest only after chronic renal failure has turned irreversible. In recent years, several therapeutic procedures, have been developed. They are of therapeutic significance for the early stages of the disease as well. Observing especially conditions renal transplantation or combined hepatorenal transplantation can be managed with a successful outcome. As the perioxisomal enzyme is activated only in the liver cells, an early liver transplantation as a definitive treatment by enzyme replacement may be the successful therapy in the future.

Alanine glyoxylate aminotransferase and the urinary excretion of oxalate and glycollate in hyperoxaluria type I and the Zellweger syndrome

We have studied the urinary excretion of oxalate and glycollate in patients with the Zellweger syndrome and hyperoxaluria type I and have measured the activity of alanine glyoxylate aminotransferase (a peroxisomal enzyme in man) in the patients. In agreement with earlier reports we found that alanine glyoxylate aminotransferase was strongly deficient in liver from a hyperoxaluria type I patient, thus explaining the increased urinary excretion of oxalate and glycollate in these patients. In livers from Zellweger patients, however, in which morphologically distinguishable peroxisomes are absent, the enzyme was not deficient, which is in accordance with our finding that the urinary excretion of oxalate and glycollate was normal in these patients.

Enzymological diagnosis of primary hyperoxaluria type 1 by measurement of hepatic alanine: glyoxylate aminotransferase activity

A deficiency of activity of the peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT,EC 2.6.1.44)has been found in the livers of six patients with primary hyperoxaluria type 1 (PH), including three in whom the tissue was obtained by percutaneous needle biopsy. AGT activity, assayed in unfractionated liver tissue, ranged from 11 to 47% of the mean control value, and appeared to be related to the clinical severity of PH and to several biochemical variables which indicate the degree of pathophysiological derangement. There was no difference between patients and controls in the activities of glutamate: glyoxylate aminotransferase (GGT, EC 2.6.1.4) or catalase (EC 1.11.1.6). In the five most severe cases residual AGT activity could be largely accounted for by the crossover from another enzyme, presumably GGT. PH can be diagnosed using percutaneous hepatic needle biopsy and assay of AGT, whose activity may be useful in determining the prognosis and likely severity of the disease.

Peroxisomal alanine:glyoxylate aminotransferase deficiency in primary hyperoxaluria type I

Activities of alanine:glyoxylate aminotransferase in the livers of two patients with primary hyperoxaluria type I were substantially lower than those found in five control human livers. Detailed subcellular fractionation of one of the hyperoxaluric livers, compared with a control liver, showed that there was a complete absence of peroxisomal alanine:glyoxylate aminotransferase. This enzyme deficiency explains most of the biochemical characteristics of the disease and means that primary hyperoxaluria type I should be added to the rather select list of peroxisomal disorders.

Potential biosoluble carriers: biocompatibility and biodegradability of oxidized cellulose

The biocompatibility and biodegradability of periodate oxidized cellulose is assessed in vivo. Morophological and histopathological studies over a period of six months indicate that oxidized cellulose degrades slowly without producing excessive tissue reaction. Preliminary investigations on the kinetics of degradation of oxidized cellulose in vitro, immobilization of alpha-chymotrypsin on it and the rate of the enzyme release in a solution of pH 7.4 are also briefly reported.