Coordinately increased lysozymuria and lysosomal enzymuria induced by maleic acid

Profiling transcriptomes of human SH-SY5Y neuroblastoma cells exposed to maleic acid

Background

Maleic acid is a multi-functional chemical widely used in the field of industrial chemistry for producing food additives and food contact materials. As maleic acid may contaminate food by the release from food packages or intentional addition, it raises the concern about the effects of excessive dietary exposure to maleic acid on human health. However, the influence of maleic acid on human health has not been thoroughly studied. In silico toxicogenomics approaches have found the association between maleic acid and nervous system disease in human. The aim of this study is to experimentally explore the effects of maleic acid on human neuronal cells.

Methods

A microarray-based transcriptome profiling was performed to offer a better understanding of the effects of maleic acid on human health. Gene expression profiles of human neuroblastoma SH-SY5Y cells exposed to three concentrations of maleic acid (10, 50, and 100 μM) for 24 h were analyzed. Genes which were differentially expressed in dose-dependent manners were identified and further analyzed with an enrichment analysis. The expression profile of selected genes related to the inferred functional changes was validated using quantitative polymerase chain reaction (qPCR). Specific fluorescence probes were applied to observe the inferred functional changes in maleic acid-treated neuronal cells.

Results

A total of 316 differentially expressed genes (141 upregulated and 175 downregulated) were identified in response to the treatment of maleic acid. The enrichment analysis showed that DNA binding and metal ion binding were the significant molecular functions (MFs) of the neuronal cells affected by maleic acid. Maleic acid exposure decreased the expression of genes associated with calcium and thiol levels of the cells in a dose-dependent manner. The levels of intracellular calcium and thiol levels were also affected by maleic acid dose-dependent.

Discussion

The exposure to maleic acid is found to decrease the cellular calcium and thiol levels in human neuronal cells at both transcriptional and functional levels. This study reported the first transcriptomic profiling of human neuronal cells treated with maleic acid. It is also the first experimental validation of chemical effects predicted by in silico toxicogenomics approaches. The proposed approach may be useful in understanding the potential effects of other poorly characterized chemicals on human health.

The urinary proteome and metabonome differ from normal in adults with mitochondrial disease

We studied the extent and nature of renal involvement in a cohort of 117 adult patients with mitochondrial disease, by measuring urinary retinol-binding protein (RBP) and albumin; established markers of tubular and glomerular dysfunction, respectively. Seventy-five patients had the m.3243A>G mutation and the most frequent phenotypes within the entire cohort were 14 with MELAS, 33 with MIDD, and 17 with MERRF. Urinary RBP was increased in 29 of 75 of m.3243A>G patients, whereas albumin was increased in 23 of the 75. The corresponding numbers were 16 and 14, respectively, in the 42 non-m.3243A>G patients. RBP and albumin were higher in diabetic m.3243A>G patients than in nondiabetics, but there were no significant differences across the three major clinical phenotypes. The urine proteome (mass spectrometry) and metabonome (nuclear magnetic resonance) in a subset of the m.3243A>G patients were markedly different from controls, with the most significant alterations occurring in lysosomal proteins, calcium-binding proteins, and antioxidant defenses. Differences were also found between asymptomatic m.3243A>G carriers and controls. No patients had an elevated serum creatinine level, but 14% had hyponatremia, 10% had hypophosphatemia, and 14% had hypomagnesemia. Thus, abnormalities in kidney function are common in adults with mitochondrial disease, exist in the absence of elevated serum creatinine, and are not solely explained by diabetes.

An in silico toxicogenomics approach for inferring potential diseases associated with maleic acid

Maleic acid is a multi-functional chemical widely applied in the manufacturing of polymer products including food packaging. However, the contamination of maleic acid in modified starch has raised the concerns about the effects of chronic exposure to maleic acid on human health. This study proposed a novel toxicogenomics approach for inferring functions, pathways and diseases potentially affected by maleic acid on humans by using known interactions between maleic acid and proteins. Neuronal signal transmission and cell metabolism were identified to be most influenced by maleic acid in this study. The top disease categories inferred to be associated with maleic acid were mental disorder, nervous system diseases, cardiovascular diseases, and cancers. The results from the in silico analysis showed that maleic acid could penetrate the blood-brain barrier to affect the nervous system. Several functions and pathways were further analyzed and identified to give insights into the mechanisms of maleic acid-associated diseases. The toxicogenomics approach may offer both a better understanding of the potential risks of maleic-acid exposure to humans and a direction for future toxicological investigation.

Urinary enzyme evaluation of nephrotoxicity in the dog

Over the past 20 yr, increased attention has been directed toward evaluation of urinary enzymes as markers of nephrotoxicity in dogs because the technique is noninvasive and considered to be more sensitive than the more commonly used conventional tests of renal function. Urinary enzymes also have the potential of determining the primary site of renal damage because different sections of the nephron have a characteristic complement of enzymes. In dogs, increases in brush border enzymes, including gamma-glutamyl transferase and alkaline phosphatase, have been associated with renal proximal tubular damage, while increases in N-acetyl-beta-D-glucosaminidase have been observed in the early stage of renal papillary necrosis. Urinary enzymes have been particularly useful in detection of acute renal damage in dogs, specifically tubular damage: however, their corresponding value in providing information about chronic renal damage remains to be established. Although elevation of certain enzymes appears to be a relatively sensitive measure of nephrotoxicity in the dog, there is no current agreement regarding which enzyme assays are the most appropriate for routine use in safety assessment studies. In addition, elevation of a single enzyme is of limited diagnostic value in detection of renal damage because spurious increases in urinary enzymes sometimes occur in normal dogs. Therefore, if one wishes to conduct special assessment of nephrotoxicity in dogs, evaluation of several enzymes at multiple time points is needed to compensate for normal enzyme variation and to identify potential anatomic site selectivity of the toxin.

Insights into the biochemical mechanism of maleic acid-induced Fanconi syndrome

Maleic acid administration is known to produce the Fanconi syndrome, although the biochemical mechanism is incompletely understood. In this study the effect of a single injection of maleic acid (50 mg/kg body wt, i.v.) on the rat renal ATPases was examined. Maleic acid rapidly caused bicarbonaturia, natriuresis, and kaliuresis. When nephron segments were microdissected, there was an 81 +/- 2% reduction in proximal convoluted tubule (PCT) Na-K-ATPase activity (P < 0.005) and a 48 +/- 4% reduction in PCT H-ATPase activity (P < 0.01). Enzyme activity (Na-K-ATPase, H-ATPase, H-K-ATPase) in the medullary thick ascending limb of Henle's loop and distal nephron segments was normal. In vitro, maleic acid (1 and 10 mM) inhibited Na-K-ATPase in PCT, but it had no effect on H-ATPase in PCT. Prior phosphate infusion to maleic acid-treated rats attenuated urinary bicarbonate wastage by 50% (P < 0.05); activity of proximal tubule Na-K-ATPase and H-ATPase activities were partially protected as compared to the animals given maleic acid alone (P < 0.05). Renal cortical ATP levels were not altered at the concentration of maleic acid used in this study (that is, 50 mg/kg body wt), but higher doses of maleic acid (that is, 500 and 1000 mg/kg body wt) caused ATP levels to fall. Maleic acid did not affect cortical medullary total phosphate concentration, however, P32 turnover (1 and 24 hr) was altered by prior phosphate infusion. A protective effect of prior phosphate loading on the membrane bound Pi pool (insoluble) was seen while the cytosolic Pi pool (soluble) was not different from control. Thus, maleic acid-induced "Fanconi" syndrome likely results from both direct inhibition of proximal tubule Na-K-ATPase activity and membrane-bound phosphorus depletion. The former mechanism would reduce activity of the sodium-dependent transporters (that is, Na/H antiporter), while the latter would inhibit the electrogenic proton pump (H-ATPase). The combination of reduced proximal tubule Na-H exchange and H-ATPase activities would markedly inhibit bicarbonate reabsorption and result in the metabolic acidosis universally seen in the Fanconi syndrome.

Osteomalacia associated with adult Fanconi's syndrome: clinical and diagnostic features

OBJECTIVE

Osteomalacia associated with adult acquired Fanconi's syndrome is thought to result from hypophosphataemia and relative 1,25-dihydroxyvitamin D deficiency. We have followed the clinical and diagnostic features of patients with osteomalacia associated with adult Fanconi's syndrome, with particular emphasis on their responses to treatment with calcium, phosphate and vitamin D.

DESIGN

Retrospective Mayo Clinic case-note review from 1975 to 1994 and prospective follow-up study, combined with literature review.

PATIENTS

Eleven patients (7 male, 4 female) were identified who satisfied criteria for diagnosis of osteomalacia and adult Fanconi's syndrome. Twenty-five additional patients were identified in a literature review from 1954 to the present.

METHODS

Clinical history and physical examination, serum and urine bone and mineral parameter, X-ray radiography and iliac crest bone histomorphometry.

RESULTS

All patients presented with typical symptoms of osteomalacia, including lower extremity or low back bone pain, and all had fractures, pseudofractures, and/or bone demineralization on X-ray radiography. Osteomalacia and Fanconi's syndrome were diagnosed concurrently in 10 patients, whereas osteomalacia preceded diagnosis of Fanconi's syndrome by 5 years in one patient. Pre-treatment bone biopsies in 9 of the 11 patients demonstrated increased osteoid surface, volume and width. In the one patient labelled with tetracycline prior to biopsy, mineralization lag time was prolonged at 111 days (normal 19.2 +/- 1.0 days). Hypophosphataemia, inappropriately low 1,25-dihydroxyvitamin D levels, renal insufficiency, and chronic acidosis due to bicarbonate leak and uraemia, contributed to the osteomalacia in these patients. Secondary hyperparathyroidism was present in two patients. Eight of the 11 patients with osteomalacia associated with Fanconi's syndrome had monoclonal disorders, including multiple myeloma or lymphoma, many of them manifest by light-chain proteinuria. Over a mean patient follow-up period of 46 months (range 1-239 months), patients responded symptomatically to calcium, phosphate, and vitamin D replacement typically within 1-6 months. In 8 patients in whom follow-up data were available, post-treatment serum phosphate and 1,25-dihydroxyvitamin D levels improved in the setting of stable mild renal insufficiency; only one patient developed end-stage renal failure after 20 years, suggesting that these patients do not invariably progress rapidly to renal failure.

CONCLUSIONS

Regardless of the underlying cause, osteomalacia associated with adult acquired Fanconi's syndrome appears to respond well to calcium, phosphate, and vitamin D replacement. These patients do not appear to necessarily require 1,25-dihydroxyvitamin D replacement.

Diseases of renal adenosine triphosphatase

Most renal transport is a primary or secondary result of the action of one of three membrane bound ion translocating ATPase pumps. The proximal tubule mechanisms for the reabsorption of salt, volume, organic compounds, phosphate, and most bicarbonate reabsorption depend upon the generation and maintenance of a low intracellular sodium concentration by the basolateral membrane Na-K-ATPase pump. The reabsorption of fluid and salt in the loop of Henle is similarly dependent on the energy provided by Na-K-ATPase activity. Some proximal tubule bicarbonate reabsorption and all distal nephron proton excretion is a product of one of two proton translocating ATPase pumps, either an electrogenic H-ATPase or an electroneutral H-K-ATPase. In this article, the authors review the biochemistry and physiology of pump activity and consider the pathophysiology of proximal and distal renal tubular acidosis, the Fanconi syndrome, and Bartter's syndrome as disorders of ATPase pump function.

Peritubular Na-K exchange ion pump in maleate-treated frog kidney proximal tubular cells

1. After perfusion of isolated frog kidneys for 1 hr with 10(-3) or 10(-2) M maleate Ringer, the peritubular membrane potential gradually declined in a dose-dependent manner. 2. The ouabain-like effects of maleate on cell Na and K activities were dose-dependent and smaller than the effects of zero K or 10(-4) M ouabain. Intracellular pH was not altered in the presence of 10(-2) M maleate. 3. The driving force for Na entry into the cell was reduced, respectively, to 81.4 and 58.4% (of control) in the presence of 10(-3) and 10(-2) M maleate. 4. There was no histochemically detectable inhibition of proximal tubule Na-K ATPase activity during 3 hr of perfusion with 10(-2) M maleate.