Luminal transport step of para-aminohippurate (PAH): transport from PAH-loaded proximal tubular cells into the tubular lumen of the rat kidney in vivo

 Proximal tubular cells were loaded for 10 s with [³H]para-aminohippurate ([³H]PAH) by microperfusing the peritubular capillaries with Ringer solution containing 0.05 mmol/l PAH. Immediately thereafter [³H]PAH influx from cells into a column of equilibrium solution injected into the oil-filled tubular lumen was measured by re-aspirating the fluid after 1–10 s of contact time. The rise of luminal PAH concentration within 2 s of contact time was almost linear, reaching a luminal / capillary concentation ratio of 1.6 after 2 s and of 3.2 after 5 s. The 2-s PAH concentration ratio was not changed when different manoeuvres were applied to depolarize proximal tubular cells. Also, the 2-s PAH concentration ratio was not influenced by varying the luminal pH from 6.0 to 8.0 or the luminal Cl^–concentration from zero to 134 mmol/l or when either 5 mmol/l urate or 25 mmol/l lactate was in the luminal perfusate. A decrease in the 2-s PAH concentration ratio, i.e. trans-inhibition, was observed when 25 or 50 mmol/l HCO₃ ^–(–50%) was in the luminal perfusate. Trans-inhibition was also seen with 5 mmol/l of the following substituted benzoates: 2-hydroxy-benzoate (–58%), 2-methoxy-benzoate (–46%), 2-hydroxy-benzoate-acetyl ester (–36%), 2-hydroxy-3,5-dinitro-benzoate (–48%), 3,5-dichloro-benzoate (–49%), and 2,3,5-trichloro-benzoate (–45%). No effect was seen with benzoate, 3-hydroxy-benzoate, 2-chloro-benzoate, 2-nitro-benzoate, 2,5-dinitro-benzoate, 3-sulfamoyl-benzoate and 4-sulfamoyl-benzoate. However, analogues of the latter two compounds possessing two additional side groups, such as furosemide and piretanide, or a hydrophobic moiety, such as probenecid, were inhibitory (by –62, –41 and –49% respectively). Phenoxyacetate had no effect; however, it inhibited if in addition it had three chloro groups, as in 2,4,5-trichlorophenoxyacetate (–71%) or a hydrophobic carbamoyl side group, as in mersalylic acid (salyrgan, –75%). Benzene-sulfonate trans-inhibited (–33%), as did phenolsulfonphthalein (phenol red, –39%) and sulfofluorescein (–55%). However, the trans-inhibitory effect of the corresponding carboxy-compounds was absent (phenolphthalein) or weaker (fluorescein, –42%). The trans-inhibitory effect of the uricosurics ethacrynic acid (–53%), tienilic acid (–55%) indacrinone (–72%) and benzbromarone (–42%) could be attributed to two chloro or bromo side groups on the benzene ring. Other trans-inhibiting uricosuric substances were indomethacin (–42%), sulfinpyrazone (–38%), losartan (–80%) its metabolite EXP 3174 (–55%), and AA 193 (–65%). These organic acids, with pKa values between 2.8 and 4.9, possess chloro and sulfin groups, as well as heterocyclic 5-ring and hydrophobic ring or chain areas. No significant effect was seen with 5 mmol/l PAH, 2-oxo-glutarate, DIDS, cGMP, prostaglandin E₂, cortisol, benzylamiloride, pyrazinoic acid and 25 mmol/l lactate. Our data indicate that in situ the secretory luminal PAH transport proceeds in a non-rheogenic fashion, per exclusionem by anion exchange. The observed trans-inhibition of PAH secretion seems to correlate with the affinity for the luminal PAH transporter and, for uricosuric substances, with their uricosuric potency. Received: 15 October 1996 / Received after revision: 17 December 1996 / Accepted: 18 December 1996     

Effects of SITS on urate transport by isolated,perfused snake renal tubules

Effects of an inhibitor of membrane anion-exchange transport processes, 4-acetamido-4-isothiocyano-2,2-disulfonic stilbene (SITS), on urate transport by isolated, perfused snake (Thamnophis spp.) proximal renal tubules were studied. SITS (10^–4 mol/l) in the luminal perfusate had absolutely no effect on net urate secretion (J _urate ^net ) or on net fluid absorption (J _v). This observation is compatible with other data that give no support to the concept of a mediated transport step for urate from the cells to the lumen. SITS (10^–4 mol/l) in the bathing medium reversibly inhibitedJ _urate ^net without affectingJ _v. At the time of maximum inhibition ofJ _urate ^net , the concentration of urate in the cell water was increased and the apparent permeability of the luminal membrane to urate was decreased, but the urate efflux across the peritubular membrane and the apparent permeability of the peritubular membrane to urate were unchanged. There was no evidence of significant intracellular binding or trapping of urate. Although an increase in the initial rate of urate transport into the cells across the peritubular membrane could not be demonstrated conclusively in nonperfused tubules, the results still suggest that SITS in the bathing medium may inhibitJ _urate ^net by inhibiting urate movement from the cells to the lumen while actually enhancing transport from the bathing medium into the cells.     

Renal urate transport during variations in urate synthesis in the rat

Summary In order to determine the effect of intrarenal synthesis of urate upon the urinary urate excretion in the rat, we effected large changes in urate synthesis by increasing it with hypoxanthine and decreasing it with allopurinol. Hypoxanthine infusion increased plasma urate rapidly and also increased the urinary urate excretion and its renal clearance. However, when the plasma urate was maintained constant, hypoxanthine had no effect upon renal urate transport. Conversely, allopurinol infusion rapidly diminished the plasma urate, urinary urate excretion and its renal clearance. Again, the maintenance of a constant plasma urate concentration prevented any change in urate transport during allopurinol. The urinary degradative purine metabolite pattern was altered pre-dictably by hypoxanthine and allopurinol. Assuming that any putative intrarenal component of urate synthesis would be affected predictably and consistently by hypoxanthine and allopurinol, these results suggest that changes in intrarenal urate synthesis are not an important determinant of urate excretion in the rat.Reported in abstract form in Clinical Research23, 508 A (1975)     

Urate predicts subsequent cardiac death in stroke survivors.

AIMS: To test the hypothesis that urate predicts cardiac death after stroke independent of conventional risk factors of atherosclerosis, creatinine and diuretic use. METHODS AND RESULTS: Serum urate concentration was measured in an unselected cohort of 354 stroke survivors who were followed-up for a median of 2.8 years. Cardiac death was the primary end-point. Urate was associated with a statistically significant threefold increase in relative risk of cardiac death even after adjustment for other conventional risk factors. In the subgroup of patients who were not on diuretics, raised urate was associated with a 12-fold significant increase in relative risk of cardiac death after adjusting for renal function and other conventional risk factors. A urate concentration of greater than 0.31 mmol. l(-1) was 78% sensitive at predicting cardiac death within 5 years after stroke, but was only 54% specific. If urate exceeded 0.38 mmol. l(-1), specificity of predicting cardiac death within 5 years after stroke was 88%. CONCLUSIONS: Elevated serum urate concentration may be used to stratify risk of future cardiac death after stroke. This appeared to be true even in stroke survivors who were not on diuretic therapy.     

一种新型尿酸氧化酶四聚体提取纯化方法的建立

目的 建立一种简便、快速的尿酸氧化酶四聚体提取纯化的方法,以适应大规模生产需求。方法 首先通过基因工程的方法获得可以稳定发酵生产尿酸氧化酶的大肠埃希菌菌株,再通过一步萃取法从破碎菌体沉淀中获得尿酸氧化酶蛋白混合物,通过硫酸铵沉淀、离子交换和分子筛层析,最终获得纯化的活性尿酸氧化酶四聚体。结果 通过优化发酵及提取条件,每升发酵液可得到尿酸氧化酶四聚体蛋白约400 mg,其纯度>95%,比活>10 U/mg。结论 建立了一种新的尿酸氧化酶四聚体高效提取纯化的方法。     

Serum urate levels are unchanged with continuous positive airway pressure therapy for obstructive sleep apnea: a randomized controlled trial

ObjectiveHyperuricemia is associated with the presence and severity of obstructive sleep apnea (OSA). Previous work has shown that treatment of OSA with continuous positive airway pressure (CPAP) therapy reduces urinary uric acid excretion and serum urate, but there has been no previous randomized controlled investigation on the effects of CPAP therapy on serum urate; we aimed to assess this association.MethodsSerum urate was measured in samples from participants of a previously published randomized controlled trial. Samples were taken at baseline and after 3 months from men with known type 2 diabetes mellitus (T2DM) and newly diagnosed OSA, randomized to receive either therapeutic (n = 19) or placebo (n = 19) CPAP for 3 months.ResultsBoth groups were well matched at baseline, with no significant difference in age, body mass index (BMI), glycosylated hemoglobin (HbA1c), or oxygen desaturation index (ODI). There was no significant difference in therapeutic or placebo CPAP usage. There was no significant difference in urate levels between groups at baseline (362 μmol/L [standard deviation {SD}, 96] vs 413 μmol/L [SD, 91] [reference range, 110–428 μmol/L]) or at 3 months. Baseline urate did not correlate with ODI, BMI, or HbA1c. The mean change in urate at 3 months did not significantly differ between treatment groups (−7.6 μmol/L [SD, 35.9] vs −6.2 μmol/L [SD, 46.2]) (P = .9; [95% confidence interval, −28.7 to +25.9]).ConclusionOur randomized controlled trial has shown no significant reduction in serum urate following 3 months treatment with therapeutic or placebo CPAP.     

Urate transport in health and disease

Circulation of urate levels is determined by the balance between urate production and excretion, homeostasis regulated by the function of urate transporters in key epithelial tissues and cell types. Our understanding of these physiological processes and identification of the genes encoding the urate transporters has advanced significantly, leading to a greater ability to predict risk for urate-associated diseases and identify new therapeutics that directly target urate transport. Here, we review the identified urate transporters and their organization and function in the renal tubule, the intestinal enterocytes, and other important cell types to provide a fuller understanding of the complicated process of urate homeostasis and its role in human diseases. Furthermore, we review the genetic tools that provide an unbiased catalyst for transporter identification as well as discuss the role of transporters in determining the observed significant gender differences in urate-associated disease risk.     

Is serum uric acid related to non-motor symptoms in de-novo Parkinson's disease patients?

BackgroundLow serum uric acid (UA) has been consistently shown to be associated with increased risk of Parkinson's disease (PD), and to predict faster motor and cognitive decline in established PD. The aim of the present study is to evaluate the relationship between serum UA and non-motor symptoms (NMS) in de novo PD.MethodsSerum UA was measured in consecutively recruited, early drug-naïve PD patients. Exclusion criteria were: treatment with UA modifying drugs; current smoking status; metabolic or cardiac morbidity. All patients completed the NMS Questionnaire (NMSQuest). The relationship between UA levels and NMSQuest domains was explored by logistic regression, subsequently adjusted for age, gender, disease duration (months since reported motor onset) UPDRS part III, H&Y scale, and MMSE. Regression analysis studied the overall relationship between UA levels and total NMS score, and was subsequently adjusted for age, gender, disease duration UPDRS part III, H&Y scale and MMSE.ResultsEighty PD patients were recruited. At logistic regression, higher UA levels were related to lower involvement of Attention/Memory (p = 0.004), Cardiovascular (0.009) and Sleep (p = 0.028) domains of NMSQuest. UA levels showed a significant negative correlation with total NMSQuest score at regression analysis (p = 0.001; Adjusted R-squared = 0.319).DiscussionThe present study investigated, for the first time, the relationship between NMSQuest and UA in de novo PD. Lower UA was related to higher NMSQuest total score and in particular to Attention/Memory, Cardiovascular and Sleep domains. Thus, UA seems to be a major candidate to be a valuable biomarker of such early features of PD as NMS.