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For herbivorous insects, dietary sources of low molecular weight non-enzymatic antioxidants, such as ascorbic acid, may influence performance in the presence of phototoxic plant constituents. We examined responses of Trichoplusia ni, a broad generalist, and Depressaria pastinacella, a specialist on furanocoumarin-containing plants, to variation in dietary ascorbic acid availability in the presence and absence of xanthotoxin, a phototoxic furanocoumarin. In T. ni, dietary ascorbic acid significantly increased levels of this compound in body tissues (approximately 7-fold, 5-fold, and 8-fold in hemolymph, gut, and fat body, respectively). In the presence of xanthotoxin, however, the amount of ascorbic acid accumulated significantly decreased. This decrease was not due to antifeedant effects of xanthotoxin and may instead have resulted from depletion of ascorbic acid due to its radical scavenging activity. In contrast, ascorbic acid levels in D. pastinacella were less affected by variation in dietary levels of either xanthotoxin or ascorbic acid, although uric acid, another potential water-soluble nonenzymatic antioxidant, increased in response to dietary ascorbic acid, as it did in T. ni. Thus, for generalists, such as T. ni, that lack specialized detoxification mechanisms against phototoxins such as furanocoumarins, dietary ascorbic acid may play an important role in antioxidant defense, and, for caterpillars in general, uric acid may also contribute to antioxidant defenses. Arch. Copyright 1999 Wiley-Liss, Inc.
Uric acid in serum was determined calorimetrically with a batch type microcalorimeter, by measuring the heat evolved during a coupled uricase/catalase enzymic reaction in tris(hydroxymethyl)aminomethane HCl buffer (pH 9.0 at 30 degrees C). Heat evolution and concentration are linearly related through the physiological range of serum uric acid concentrations and the method is free of interferences of the sort encountered with spectrophotometric methods. Precision and accuracy are good (CV, 2%) and the results correlate well with those obtained by a mechanized colorimetric uricase/peroxidase system.
INTRODUCTION: In the Olympus uric acid procedure, uric acid is converted by uricase to allantoin and hydrogen peroxide, which is reacted in a Trinder reaction to produce a chromophore read bichromatically at 520 and 660 nm. Repeated difficulty was encountered in obtaining uric acid results on samples from myeloma patients with known IgM paraproteins. Large absorbances in sample blanks were due to a visible precipitation observed in the reaction cuvettes. OBJECTIVE: To alter the Olympus method (OM) to eliminate the interference by IgM, and to verify the modified method (MM). METHODS: Dilution of the sample blank by saline was substituted for water in the MM, with small alterations in the reaction timing sequence necessary to accommodate the instrument requirements. RESULTS: A comparison of uric acid results obtained from nonmyeloma patient samples using the OM and the MM showed a good correlation (r = 0.970), and no statistical difference between the two means using a paired t-test. A similar comparison performed using the samples containing IgA and IgG paraproteins also revealed a good correlation (r = 0.981), and no statistical difference between the two means. Results on IgM containing specimens were assessed indirectly because the samples could not be assayed with the OM. First, removal of detectable levels of proteins using a 20% TCA solution did not affect the measurement of uric acid. Second, protein-free supernatants from IgM containing samples were measured by the OM and compared with the corresponding serum samples measured by the MM. There was good correlation between the two methods (r = 0.945), and no statistical difference between the means using a paired t-test. CONCLUSION: The modified method is satisfactory for routine analysis of samples, including those with IgM paraproteins.
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Dissolution of uric acid calculi was studied in vitro. Calculated rate constants were then applied to an in vivo situation. The time required for complete dissolution of a uric acid calculus in a patient on oral alkali therapy can be estimated. Sodium bicarbonate, acetylcysteine, [tris(hydroxymethyl)aminomethane] and [tris(hydroxymethyl)aminomethane]-E were tested for relative effectiveness in dissolving uric acid calculi in vitro. In patients who require irrigation for dissolution of uric acid calculi [tris(hydroxymethyl)-aminomethane] is the preferred agent.
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BACKGROUND: Deposition of uric acid in the kidney can lead to progressive tubulointerstitial injury with granuloma formation. We hypothesized that uric acid crystal deposition may induce granuloma formation by stimulating local expression of macrophage migration inhibitory factor (MIF), which is a known mediator of delayed type hypersensitivity (DTH). MATERIALS AND METHODS: A model of acute uric acid nephropathy was induced in rats by the administration of oxonic acid (an inhibitor of uricase), together with uric acid supplements. MIF expression and local cellular response were examined by in situ hybridization and immunohistochemistry. RESULTS: Kidney tissue examined at 35 days posttreatment showed widespread tubulointerstitial damage with intratubular uric acid crystal deposition and granuloma formation. Tubules within the areas of granuloma showed a six-fold increase in MIF mRNA, compared with uninvolved areas by in situ hybridization. Moreover, the areas of increased MIF mRNA expression correlated with sites of dense accumulation of macrophages and T cells, and these cells were activated when assessed by the expression of interleukin-2R (IL-2R) and (MHC) class II. Interestingly, cytoplasmic staining for MIF protein in the uric acid (UA) crystal-associated granulomatous lesions was reduced, indicating a rapid MIF secretion by damaged tubules and macrophages secondary to uric acid crystal stimulation. This was confirmed by the demonstration of a marked increase in urinary MIF protein by Western blot analysis. Control rats fed either a normal diet or only oxonic acid had no discernible evidence of renal disease by routine light microscopy and minimal tubular expression of MIF mRNA and protein. CONCLUSIONS: These data suggest that intrarenal granulomas in urate nephropathy may be the consequence of a crystal induced DTH reaction mediated by MIF.
Uric acid is known to be an end product of purine metabolism. Increases in uric acid may be found in clinical conditions associated with tissue hypoxia. We have investigated the value of uric acid to differentiate between a transudate and exudate. In this study, we measured uric acid in the pleural fluid and the serum of 110 patients, 30 women and 80 men with a mean age of 49.5+/-19 years. Light's criteria were used to differentiate between a transudate and exudate. Mean serum uric acid was 496.7+/-153.4 micromol/l in patients with transudates and 291.3+/-143.1 micromol/l in patients with exudates. Mean pleural fluid uric acid was 487.7+/-165 micromol/l in patients with transudates and 279.9+/-142.1 micromol/l in patients with exudates. These data showed that the levels of serum and pleural uric acid were higher in transudates than exudates (p<0.01). However, there was no significant difference between pleural fluid/serum uric acid ratio of the two patient groups (p>0.05). The specificity and sensitivity of pleural uric acid for diagnosis of transudate effusions were 73% and 80.6%, respectively. The specificity and sensitivity of pleural uric acid for diagnosis of transudate effusions from exudates without malignancy were 71.8% and 91.7%, respectively. The sensitivity and specificity of pleural lactate dehydrogenase for diagnosis of exudates were 82% and 89%; the sensitivity and specificity of pleural fluid/serum lactate dehydrogenase were 85% and 89%; the sensitivity and specificity of pleural fluid/serum protein were 91% and 89%, respectively. Using all three of Light's criteria together, the sensitivity was 91% and its specificity was 94%. Our findings indicate that determination of uric acid in pleural fluid may be of diagnostic value in differential diagnosis of transudates and exudates. The sensitivity of pleural uric acid measurement was higher for exudates without malignancy. However, Light's criteria remain the best means of separating transudates from exudates.