Urate Synthesis Research Articles

Fatty acid oxidation-induced HIF-1α activation facilitates hepatic urate synthesis through upregulating NT5C2 and XDH

Abstract Dyslipidemia affects approximately half of all people with gout, and prior Mendelian randomization analysis suggested a causal role for elevated triglycerides in hyperuricemia (HU), but the underlying mechanisms remain elusive. We hypothesize that dyslipidemia promotes hepatic urate biosynthesis in HU and gout and fatty acid (FA) oxidation (FAO) drives this process. Here we developed a targeted metabolomics to quantify major metabolites in purine metabolic pathway in the sera of a human cohort with HU, gout, and normaluricemic controls. We found that the levels of major purine metabolites and multiple FAs were significantly elevated in HU and gout, compared to normouricemic controls, whereas hypoxathine showed opposite trend. Furthermore, the levels of multiple serum FAs were positively correlated with urate, xanthine, and inosine but negatively with hypoxanthine, which was also observed in a murine model of high-fat diet-induced HU. Using a stable isotope labeled metabolic flux assay, we discovered that exogenous hypoxanthine plays a key role in urate synthesis. Moreover, FAO-induced hypoxia-inducible factor 1 alpha (HIF-1α) activation upregulated 5’-nucleotidase II (NT5C2) and xanthine dehydrogenase (XDH) levels to facilitate hypoxanthine uptake from blood to liver and activation of urate biosynthesis. Our findings was further supported by data in human hepatocytes and 50 paired serum and liver tissues from liver transplant donors.Together, this study uncovers a mechanism by which FAO promotes hepatic urate synthesis by activating HIF-1α-NT5C2/XDH pathways, directly linking lipid metabolism to HU.

Water-soluble hexakis-imidazolium cages: synthesis and selective binding of sodium urate

Selective binding of uric acid, the molecule that causes gout, by imidazolium-incorporated molecular cages in water.

Purine Metabolic Pathway Alterations and Serum Urate Changes after Oral Inosine Loading in Male Chinese Volunteers.

Oral inosine loading is a new method to evaluate the effects of purine on urate metabolism. However, individuals respond differently to acute purine intake, and the effects on the metabolism of other purines remain to be explored. 35 male participants are recruited. Participants received 500mg of inosine orally after an overnight fast, and blood and urine samples are collected before and at various time points over 180min after inosine administration. The serum urate concentration is significantly different between the hyperuricemia (n = 14) and non-hyperuricemia (n = 16) groups before inosine intake, but there is no in urate change after inosine intake. When grouped according to the baseline estimated glomerular filtration rate (eGFR), the increase in urate level in the high-eGFR group is significantly higher than that in the low-eGFR group (p = 0.047). The high-eGFR group showed higher levels of serum xanthine and xanthine oxidase (XOD), the key enzyme in urate synthesis, after inosine loading (p < 0.01). The increase in urate level is positively related to eGFR after oral acute inosine administration, which may have been due to a higher level of XOD.

Reduced uric acid levels in alcohol-associated liver disease mice model are associated with downregulation of hepatic urate synthesis and impaired renal reabsorption

Reduced uric acid levels in alcohol-associated liver disease mice model are associated with downregulation of hepatic urate synthesis and impaired renal reabsorption

Lactiplantibacillus plantarum enables blood urate control in mice through degradation of nucleosides in gastrointestinal tract

BackgroundLactobacillus species in gut microbiota shows great promise in alleviation of metabolic diseases. However, little is known about the molecular mechanism of how Lactobacillus interacts with metabolites in circulation. Here, using high nucleoside intake to induce hyperuricemia in mice, we investigated the improvement in systemic urate metabolism by oral administration of L. plantarum via different host pathways.ResultsGene expression analysis demonstrated that L. plantarum inhibited the activity of xanthine oxidase and purine nucleoside phosphorylase in liver to suppress urate synthesis. The gut microbiota composition did not dramatically change by oral administration of L. plantarum over 14 days, indicated by no significant difference in α and β diversities. However, multi-omic network analysis revealed that increase of L. plantarum and decrease of L. johnsonii contributed to a decrease in serum urate levels. Besides, genomic analysis and recombinant protein expression showed that three ribonucleoside hydrolases, RihA–C, in L. plantarum rapidly and cooperatively catalyzed the hydrolysis of nucleosides into nucleobases. Furthermore, the absorption of nucleobase by intestinal epithelial cells was less than that of nucleoside, which resulted in a reduction of urate generation, evidenced by the phenomenon that mice fed with nucleobase diet generated less serum urate than those fed with nucleoside diet over a period of 9-day gavage.ConclusionCollectively, our work provides substantial evidence identifying the specific role of L. plantarum in improvement of urate circulation. We highlight the importance of the enzymes RihA–C existing in L. plantarum for the urate metabolism in hyperuricemia mice induced by a high-nucleoside diet. Although the direct connection between nucleobase transport and host urate levels has not been identified, the lack of nucleobase transporter in intestinal epithelial cells might be important to decrease its absorption and metabolization for urate production, leading to the decrease of serum urate in host. These findings provide important insights into urate metabolism regulation.BbgstkDZoHsJm_QsUh-oZNVideo

Sulforaphane-driven reprogramming of gut microbiome and metabolome ameliorates the progression of hyperuricemia

IntroductionCurrently, revealing how to prevent and control hyperuricemia has become an essential public health issue. Sulforaphane hasawiderangeofapplications in the management of hyperuricemia. ObjectiveThe study objective was to verify the uric acid-lowering effects and the regulation of the gut-kidney axis mediated by sulforaphane and identify host-microbial co-metabolites in hyperuricemia. MethodsA hyperuricemia model was established by administering feedstuffs with 4% potassium oxonate and 20% yeast. Forty male Sprague–Dawley rats were randomly divided into the normal control, hyperuricemia, allopurinol, and sulforaphane groups. Animals were treated by oral gavage for six consecutive weeks, and then phenotypic parameters, metabolomic profiling, and metagenomicsequencing were performed. ResultsSulforaphane could lower uric acid by decreasing urate synthesis and increasing renal urate excretion in hyperuricemic rats (P＜0.05). We identified succinic acid and oxoglutaric acid as critical host-gut microbiome co-metabolites. Moreover, sulforaphane improved the diversity of microbial ecosystems and functions, as well as metabolic control of the kidney. Notably, sulforaphane exerted its renoprotective effect through epigenetic modification of Nrf2 and interaction between gut microbiota and epigenetic modification in hyperuricemic rats. ConclusionWe revealed that sulforaphane could ameliorate the progression of hyperuricemia by reprogramming the gut microbiome and metabolome. Our findings may provide a good means for efficiently preventing and treating hyperuricemia.

Uric Acid and Genetic Polymorphisms in the SLC2A9 and Xanthine Oxidase Genes in Patients with Type 2 Diabetes Mellitus in Jordan: A Cross‐sectional Study

Type 2 diabetes mellitus (T2DM) is rapidly increasing in prevalence. T2DM is defined by elevated blood glucose levels that occur as a result of cellular resistance to insulin action. Prediabetes, or poor glucose tolerance, is a pre‐diabetes condition. Prediabetes is reversible, and active intervention programs involving dietary and lifestyle changes may help prevent prediabetes from progressing to type 2 diabetes. A few studies found a favorable correlation between increased serum uric acid levels and type 2 diabetes, whereas others found no correlation or even a negative correlation. Jordan never put the aforementioned relationship under investigation. Our research focuses on comparing the serum uric acid levels in Jordan's non‐diabetic, prediabetic, and diabetic population groups (study IRB# 313/2020). Increased uric acid levels could be due to increased urate synthesis or decreased urate excretion. In humans, xanthine oxidase, a cytoplasmic enzyme, catalyzes the final two steps of purine breakdown. The oxidation of hypoxanthine to xanthine and then to uric acid is catalyzed by xanthine oxidase. The SLC2A9 gene encodes a membrane protein that is expressed in proximal renal tubular cells and functions in the excretion of urate. Numerous single nucleotide polymorphisms (SNPs) in the xanthine oxidase and SLC2A9 genes may affect the degree of expression or activity of their protein products. The connection between certain SNPs in the xanthine oxidase or SLC2A9 genes and T2DM has not been investigated in Jordan. Therefore, we aimed to study certain SNPs of the aforementioned genes in our study population and correlate the genetic analysis with the uric acid levels and the disease progression. Our results reveal the correlation between serum uric acid levels and T2DM and demonstrates if serum urate levels and SNPs affecting its synthesis or excretion may serve as early indicators of type 2 diabetes in Jordan.

Taxonomic variations in the gut microbiome of gout patients with and without tophi might have a functional impact on urate metabolism

ObjectiveTo evaluate the taxonomic composition of the gut microbiome in gout patients with and without tophi formation, and predict bacterial functions that might have an impact on urate metabolism.MethodsHypervariable V3–V4 regions of the bacterial 16S rRNA gene from fecal samples of gout patients with and without tophi (n = 33 and n = 25, respectively) were sequenced and compared to fecal samples from 53 healthy controls. We explored predictive functional profiles using bioinformatics in order to identify differences in taxonomy and metabolic pathways.ResultsWe identified a microbiome characterized by the lowest richness and a higher abundance of Phascolarctobacterium, Bacteroides, Akkermansia, and Ruminococcus_gnavus_group genera in patients with gout without tophi when compared to controls. The Proteobacteria phylum and the Escherichia-Shigella genus were more abundant in patients with tophaceous gout than in controls. Fold change analysis detected nine genera enriched in healthy controls compared to gout groups (Bifidobacterium, Butyricicoccus, Oscillobacter, Ruminococcaceae_UCG_010, Lachnospiraceae_ND2007_group, Haemophilus, Ruminococcus_1, Clostridium_sensu_stricto_1, and Ruminococcaceae_UGC_013). We found that the core microbiota of both gout groups shared Bacteroides caccae, Bacteroides stercoris ATCC 43183, and Bacteroides coprocola DSM 17136. These bacteria might perform functions linked to one-carbon metabolism, nucleotide binding, amino acid biosynthesis, and purine biosynthesis. Finally, we observed differences in key bacterial enzymes involved in urate synthesis, degradation, and elimination.ConclusionOur findings revealed that taxonomic variations in the gut microbiome of gout patients with and without tophi might have a functional impact on urate metabolism.

Quantitative Prediction of Thiazole Derivatives as Potent Xanthine Oxidase Inhibitors

AbstractIn humans, xanthine oxidase (XO) is a critical rate‐limiting enzyme in biosynthesis of uric acid. Moreover, XO is the most promising target to control uric acid levels and the treat of hyperuricemia and gout. However, XO inhibitors can effectively treat gout through the inhibition of urate synthesis, and by impairing the conversion of hypoxanthine and xanthine to uric acid. In this paper, four different quantitative structure‐activity relationship (QSAR) models of 80 thiazole derivatives were constructed to comprehend chemical‐biological interactions and predict their bioactivities using GA‐MLR (Genetic Algorithm‐Multiple Linear Regression), HQSAR (Hologram Quantitative Structure Activity Relationship), Topomer CoMFA (Comparative Molecular Field Analysis) and CoMSIA (Comparative Molecular Similarity Indices Analysis) methods. Furthermore, R2 and Q2 of the obtained GA‐MLR, HQSAR, Topomer CoMFA and CoMSIA models are 0.956 and 0.911, 0.932 and 0.876, 0.946 and 0.917, 0.964 and 0.877, respectively. In addition, the external predictive values of the GA‐MLR, HQSAR, Topomer CoMFA and CoMSIA models are 0.963, 0.936, 0.973 and 0.934, respectively. Therefore, all QSAR models exhibited good prediction performances, which can be used to quantitatively evaluate bioactivity and screen new XO inhibitors. Moreover, topological charge index, atomic electronegativity and polarizability, atomic van der Waals volumes and hydrophobic van der Waals surface area are very relevant to bioactivity of thiazole derivatives.

Gout and Metabolic Syndrome: a Tangled Web.

The complexity of gout continues to unravel with each new investigation. Gout sits at the intersection of multiple intrinsically complex processes, and its prevalence, impact on healthcare costs, and association with important co-morbidities make it increasingly relevant. The association between gout and type 2 diabetes, hypertension, hyperlipidemia, cardiovascular disease, renal disease, and obesity suggest that either gout, or its necessary precursor hyperuricemia, may play an important role in the manifestations of the metabolic syndrome. In this review, we analyze the complex interconnections between gout and metabolic syndrome, by reviewing gout's physiologic and epidemiologic relationships with its major co-morbidities. Increasing evidence supports gout's association with metabolic syndrome. More specifically, both human studies and animal models suggest that hyperuricemia may play a role in promoting inflammation, hypertension and cardiovascular disease, adipogenesis and lipogenesis, insulin and glucose dysregulation, and liver disease. Fructose ingestion is associated with increased rates of hypertension, weight gain, impaired glucose tolerance, and dyslipidemia and is a key driver of urate biosynthesis. AMP kinase (AMPK) is a central regulator of processes that tend to mitigate against the metabolic syndrome. Within hepatocytes, leukocytes, and other cells, a fructose/urate metabolic loop drives key inhibitors of AMPK, including AMP deaminase and fructokinase, that may tilt the balance toward metabolic syndrome progression. Preliminary evidence suggests that agents that block the intracellular synthesis of urate may restore AMPK activity and help maintain metabolic homeostasis. Gout is both an inflammatory and a metabolic disease. With further investigation of urate's role, the possibility of proper gout management additionally mitigating metabolic syndrome is an evolving and important question.

Phenytoin Induced Changes in Glucose and Lipid Metabolism is Related to Increased Urate Synthesis

Phenytoin Induced Changes in Glucose and Lipid Metabolism is Related to Increased Urate Synthesis

Abstract 12506: Therapeutic Strategy for Efficient Reduction of Serum Uric Acid With Allopurinol versus Benzbromarone in Hyperuricemic Patients With Cardiovascular Disease ~ A Randomized Crossover Study (TERAO study) ~

Introduction: Hyperuricemia is considered to be a marker of future cardiovascular events. Uricosuric agents and urate synthesis inhibitors has been widely used in hyperuricemic patients. Hypothesis: We assessed the hypothesis that the different mechanism of these drugs has an impact on urine albumin-creatinine ratio (ACR) associated with cardiovascular risks. Methods: A total of 14 hyperuricemic patients (serum uric acid levels &gt;7 mg/dL) with cardiovascular disease were randomly assigned and treated with either benzbromarone, 25mg once daily, or allopurinol, 200 mg twice daily for 2 weeks, followed by a 2-week washout period, then a 2-week crossover phase. Results: Serum uric acid levels were comparable and similarly reduced with benzbromarone (8.4±1.1→4.8±1.3 mg/dL, P&lt;0.0001) and allopurinol (8.4±1.0→5.1±0.9 mg/dL, P&lt;0.0001). However, allopurinol significantly reduced urine ACR compared with benzbromarone (Figure 1). A logistic regression analysis revealed that influential clinical factors on reduced urine ACR were not observed except for allopurinol administration. The change of urine ACR was positively correlated with the change of urinary urate-creatinine ratio (UCR), indicating a substitution for xanthine oxidase activity (Figure 2). Conclusions: In this short-term, crossover study in hyperuricemic patients with cardiovascular disease, a treatment with xanthine oxidase inhibitor resulted in a reduction of urine ACR. These results represent a novel potential therapeutic approach with antioxidant strategy, which may lead to a reduction of future cardiovascular events. These preliminary findings require confirmation in larger clinical trials.

Urate synthesis and oxidative stress in phenytoin hepatotoxicity: the role of antioxidant vitamins.

Phenytoin is known to induce microsomal enzymes including xanthine oxidase which catalyzes uric acid synthesis with superoxides as byproducts, thus contributing to the oxidative stress of phenytoin hepatotoxicity. To investigate the role of antioxidant vitamins in ameliorating phenytoin induced hepatic changes through possible actions on xanthine oxidase activities as measured by urate concentration. Growing albino rats of Wistar strain were randomly divided into 8 groups of 7 rats each. Group 2, 3, 4, 5, 6, 7 and 8 were treated with phenytoin alone, phenytoin + folic acid, phenytoin + vitamin E, phenytoin + vitamin E + vitamin C, phenytoin + vitamin C, phenytoin + folic acid + vitamin E and phenytoin + vitamin E + vitamin C + folic acid respectively while animals in group 1 were given normal saline to serve as control. Serum concentrations of uric acid, albumin, total protein and the activities of aspartate and alanine aminotransferases (AST and ALT) and catalase were measured spectrophotometrically using appropriate commercial reagent kits. Result showed that administration of phenytoin alone caused significant (p < 0.05) increase in serum levels of globulin, uric acid, AST and ALT activities while the levels of albumin and catalase were reduced significantly (p < 0.05). Supplementation of phenytoin treatment with vitamins resulted in various degrees of protection. However, the elevated level of uric acid in serum was not significantly (p < 0.05) affected by any of the vitamins used and there was no significant correlation between the activities of aminotransferases and uric acid concentration in the vitamin treated animals as was observed between aminotransferases and catalase. The findings in this study suggest that antioxidant vitamins were able to ameliorate phenytoin hepatotoxic effects by improving oxidant radicals removal in the animals but would not inhibit further generation of the superoxides by xanthine oxidase activity and that xanthine oxidase may contribute significantly to the oxidative stress of phenytoin therapy.

New Therapies for Gout

Gout prevalence is increasing, yet management remains suboptimal. Fortunately, new insights into gout biology are permitting the development of novel, potentially more effective strategies for both gouty inflammation and urate lowering. Colchicine, a drug long used for gout, has been recently approved (for the first time ever) by the FDA, based on a new, safer dosing regimen. The recently appreciated centrality of IL-1β in acute gouty inflammation has prompted studies of agents blocking the IL-1β receptor or soluble IL-1β signaling (canakinumab, rilonacept, anakinra). Novel approaches to urate lowering have led to mechanism-based therapies such as urate synthesis inhibitors (febuxostat is already FDA approved and BCX4208 is in development), URAT-1 inhibitors promoting renal uric acid excretion (lesinurad), and recombinant uricase to directly catabolize urate (pegloticase). These new treatments do not obviate the need for lifestyle and dietary management, another area in which significant scientific and clinical progress has recently been made.

Hyperuricemia, Cardiovascular Disease, and the Metabolic Syndrome: Figure 1.

To the Editor: We read with great interest Dr. Neogi’s recent editorial on asymptomatic hyperuricemia1, as well as the correspondence from Drs. Marasini and Massarotti2. There are strong associations among hyperuricemia, cardiovascular disease, and the metabolic syndrome3,4. Still, the role of uric acid (UA) in the latter 2 conditions is lacking. Marasini and Massarotti state that “abdominal obesity has been found to be significantly related to serum uric acid levels probably because obesity interferes with urate synthesis and … Address correspondence to Prof. R.O. Day, Level 2, Xavier Building, St. Vincent’s Hospital, Darlinghurst NSW 2010, Australia. E-mail: R.Day{at}unsw.edu.au

Association between intronic SNP in urate-anion exchanger gene, SLC22A12, and serum uric acid levels in Japanese

Serum uric acid levels are maintained by urate synthesis and excretion. URAT1 (coded by SLC22CA12) was recently proposed to be the major absorptive urate transporter protein in the kidney regulating blood urate levels. Because genetic background is known to affect serum urate levels, we hypothesized that genetic variations in SLC22A12 may predispose humans to hyperuricemia and gout. We investigated rs893006 polymorphism (GG, GT and TT) in SLC22A12 in a total of 326 Japanese subjects. Differences in clinical characteristics among the genotype groups were tested by the analysis of variance (ANOVA). In male subjects, mean serum uric acid levels were significantly different among the three genotypes. Levels in the GG genotype subjects were the highest, followed by those with the GT and TT genotypes. However, no differences between the groups were seen in the distributions of creatinine, Fasting plasma glucose (FPG), HbA 1c, total cholesterol, triglyceride, HDL cholesterol levels or BMI. A single nucleotide polymorphism (SNP) in the urate transporter gene SLC22CA12 was found to be associated with elevated serum uric acid levels among Japanese subjects. This SNP may be an independent genetic marker for predicting hyperuricemia.

EFFECT OF CRANBERRY JUICE CONSUMPTION ON URINARY STONE RISK FACTORS

We evaluated the effect of cranberry juice on urinary stone risk factors. A total of 12 normal subjects and 12 calcium oxalate stone formers underwent 2, 7-day phases of study in random order while on a controlled metabolic diet. Subjects ingested 1 l of cranberry juice (CBJ) daily in 1 phase and 1 l of deionized water in the other phase. On the last 2 days of each phase 2, 24-hour urine collections and blood samples were obtained for stone risk factors and serum chemistries. No significant differences were found between normal subjects and stone formers in response to CBJ and, therefore, the groups were combined. CBJ significantly increased urinary calcium (from 154 to 177 mg per day, p =0.0008) and urinary oxalate (from 26.4 to 29.2 mg per day, p =0.04), thereby increasing urinary saturation of calcium oxalate by 18%. Urinary citrate was unchanged and urinary magnesium increased slightly. Urinary pH decreased (from 5.97 to 5.67, p =0.0005), and urinary ammonium, titratable acidity and net acid excretion increased during CBJ ingestion. Urinary uric acid decreased (from 544 to 442 mg per day, p <0.0001) as did serum uric acid. Thus, the urinary saturation of brushite and monosodium urate was reduced by CBJ but the amount of undissociated uric acid increased. CBJ exerts a mixed effect on urinary stone forming propensity. It reduces urinary pH likely by providing an acid load and decreases urinary uric acid perhaps by retarding urate synthesis. Overall CBJ increases the risk of calcium oxalate and uric acid stone formation but decreases the risk of brushite stones.

Synthesis of ascorbate and urate in the ovary of water buffalo

Blood flow interruption is associated with oxygen depletion and loss of factors for function and survival in downstream tissues or cells. Hypoxia and absence of gonadotropins trigger apoptosis and atresia in the ovary. We studied the antioxidant response of follicular cells to plasma deprivation in ovaries dissected from water buffalo. Aliquots of follicular fluid were aspirated from each antral follicle, before and during incubation of the ovaries at 39°C. Urate, ascorbate, retinol and α-tocopherol in the fluid were, titrated by High Performance Liquid Chromatography (HPLC) with spectrophotometric or spectrofluorimetric detection. The total antioxidant capacity of follicular fluid was determined as absorbance decrease, following addition of a source of radical chromophores. The more the incubation progressed, the higher levels of urate, ascorbate and total antioxidant capacity were found. Conversely, changes in concentration of the liposoluble antioxidants were not observed. Ascorbate synthesizing activity in the follicle was demonstrated by detecting the enzyme L-gulono-γ-lactone oxidase in microsomes prepared from granulosa cells. These cells were also analyzed for the expression of the enzyme CPP32. The enzyme level, measured as DEVD-p-nitroanilide cleaving activity, was found related with the immunoreactivity to anti-CPP32 antibodies. Negative correlation between the enzyme activity (which is known to be induced by peroxynitrite) and the follicular level of urate (which scavenges peroxynitrite) was also observed. The amount of nitrotyrosine, a product of peroxynitrite attack on proteins, was measured in follicular fluids by Enzyme Linked ImmunoSorbent Assay (ELISA). This amount was found positively correlated with the CPP32 activity, and negatively correlated with the urate level in follicular fluid. Alterations in concentrations of ascorbate or urate may be associated with oxidative stress during follicular atresia.

Gout and Hyperuricemia

Gout is recognized by sudden onsets of joint pain and swelling caused by imbalances in production and excretion of uric acid. Hyperuricemia is a risk factor for gout, however, not all patients with hyperuricemia will develop gout. Other risk factors include hypertension, renal insufficiency, obesity, excessive alcohol consumption, high purine diets, and medications such as thiazide diuretics and low dose aspirin. Management of gout and hyperuricemia can be achieved through inhibiting urate synthesis, enhancing urate excretion, or both. Medications to treat gout include NSAIDs, colchicine, and glucocorticosteroids. Chronic therapy with uricosuric agents or xanthine oxidase inhibitors may be necessary for those with recurrent attacks.

Urate Synthesis in the Blood-sucking Insect Rhodnius prolixus: STIMULATION BY HEMIN IS MEDIATED BY PROTEIN KINASE C

Hemin is a catalyst of the formation of reactive oxygen species. We proposed that hematophagous insects are exposed to intense oxidative stress because of hemoglobin hydrolysis in their midgut (Petretsky, M. D., Ribeiro, J. M. C., Atella, G. C., Masuda, H., and Oliveira, P. L. (1995) J. Biol. Chem. 270, 10893-10896). We have shown that hemin stimulates urate synthesis in the blood-sucking insect Rhodnius prolixus (Graça-Souza, A. V., Petretsky, J. H., Demasi, M., Bechara, E. J. H., and Oliveira, P. L. (1997) Free Radical Biol. Med. 22, 209-214). Once released by fat body cells, urate accumulates in the hemolymph, where this radical scavenger constitutes an important defense against blood-feeding derived oxidative stress. Incubation of Rhodnius fat bodies with okadaic acid raises the level of urate synthesis, suggesting that urate production can be controlled by protein phosphorylation/dephosphorylation. Urate synthesis is stimulated by dibutyryl cAMP and inhibited by N(2((p-bromocinnamil)amino)ethyl)-5-isoquinolinesulfonamide (H-89), an inhibitor of protein kinase A, as well as activated by the protein kinase C activator phorbol 12-myristate 13-acetate. In the presence of hemin, however, inhibition of urate synthesis by H-89 does not occur, suggesting that the hemin stimulatory effect is not mediated by protein kinase A. Calphostin C completely inhibits the hemin-induced urate production, suggesting that the triggering of urate antioxidant response depends on protein kinase C activation. This conclusion is reinforced by the observation that in fat bodies exposed to hemin, both protein kinase C activity and phosphorylation of specific endogenous polypeptides are significantly increased.