SciCombinator

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Concept: Xanthine oxidase

49

Maternal metabolic diseases increase offspring risk for low birth weight and cardiometabolic diseases in adulthood. Excess fructose consumption may confer metabolic risks for both women and their offspring. However, the direct consequences of fructose intake per se are unknown. We assessed the impact of a maternal high-fructose diet on the fetal-placental unit in mice in the absence of metabolic syndrome and determined the association between maternal serum fructose and placental uric acid levels in humans. In mice, maternal fructose consumption led to placental inefficiency, fetal growth restriction, elevated fetal serum glucose and triglyceride levels. In the placenta, fructose induced de novo uric acid synthesis by activating the activities of the enzymes AMP deaminase and xanthine oxidase. Moreover, the placentas had increased lipids and altered expression of genes that control oxidative stress. Treatment of mothers with the xanthine oxidase inhibitor allopurinol reduced placental uric acid levels, prevented placental inefficiency, and improved fetal weights and serum triglycerides. Finally, in 18 women delivering at term, maternal serum fructose levels significantly correlated with placental uric acid levels. These findings suggest that in mice, excess maternal fructose consumption impairs placental function via a xanthine oxidase/uric acid-dependent mechanism, and similar effects may occur in humans.

Concepts: Triglyceride, Fructose, Hyperuricemia, Xanthine oxidase, Metabolism, Enzyme, Gout, Uric acid

39

Xanthine oxidase (XO) is distributed in mammals largely in the liver and small intestine, but also is highly active in milk where it generates hydrogen peroxide (H2O2). Adult human saliva is low in hypoxanthine and xanthine, the substrates of XO, and high in the lactoperoxidase substrate thiocyanate, but saliva of neonates has not been examined.

Concepts: Hypoxanthine, Xanthine, Xanthine oxidase, Innate immune system, Hydrogen peroxide, Milk, Oxygen, Liver

26

The enzyme xanthine oxidoreductase (XOR) is an important source of oxygen free radicals and related postischemic injury. Xanthine dehydrogenase (XDH), the major form of XOR in tissues, can be converted to xanthine oxidase (XO) by oxidation of sulfhydryl residues or by proteolysis. The conversion of XDH to XO has been assumed to be required for radical generation and tissue injury. It is also possible that XDH could generate significant quantities of superoxide, •O2-, for cellular signaling or injury; however, this possibility and its potential ramifications have not been previously considered. To unambiguously determine if XDH can be a significant source of •O2-, experiments were performed to measure and characterize •O2- generation using XDH from chicken liver which is locked in the dehydrogenase conformation. EPR spin trapping experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) demonstrated that XDH in the presence of xanthine produces significant amounts of •O2-. NAD+ and NADH inhibited •O2- generation from XDH in a dose-dependent manner with NAD+ exhibiting greater inhibition than NADH at low physiological concentrations. Decreased amounts of NAD+ and NADH, as occur during and following tissue ischemia, enhanced •O2- generation from XDH in the presence of xanthine. It was observed that XDH-mediated oxygen radical generation markedly depressed Ca2+-ATPase activity of isolated sarcoplasmic reticulum vesicles from cardiac muscle and this was modulated by NAD+ and NADH. Thus, XDH can be an important redox-regulated source of •O2- generation in ischemic tissue, and conversion to XO is not required to activate radical formation and subsequent tissue injury.

Concepts: Free radicals, Vitamin C, Senescence, Xanthine dehydrogenase, Ischemia, Radical, Xanthine oxidase, Redox

26

Objective. The aim of this study was to evaluate the pharmacodynamics (PDs), pharmacokinetics (PKs) and safety of lesinurad (selective uric acid reabsorption inhibitor) in combination with febuxostat (xanthine oxidase inhibitor) in patients with gout.Methods. This study was a phase IB, multicentre, open-label, multiple-dose study of gout patients with serum uric acid (sUA) >8 mg/dl following washout of urate-lowering therapy with colchicine flare prophylaxis. Febuxostat 40 or 80 mg/day was administered on days 1-21, lesinurad 400 mg/day was added on days 8-14 and then lesinurad was increased to 600 mg/day on days 15-21. sUA, urine uric acid and PK profiles were evaluated at the end of each week. Safety was assessed by adverse events, laboratory tests and physical examinations.Results. Initial treatment with febuxostat 40 or 80 mg/day monotherapy resulted in 67% and 56% of subjects, respectively, achieving a sUA level <6 mg/dl. Febuxostat 40 or 80 mg/day plus lesinurad 400 or 600 mg/day resulted in 100% of subjects achieving sUA <6 mg/dl and up to 100% achieving sUA <5 mg/dl. No clinically relevant changes in the PKs of either drug were noted. The combination was well tolerated.Conclusion. The clinically important targets of sUA <6 mg/dl and <5 mg/dl are achievable in 100% of patients when combining lesinurad and febuxostat.

Concepts: Xanthine oxidase, Xanthine, Pharmacodynamics, Pharmacokinetics, Hyperuricemia, Xanthine oxidase inhibitor, Gout, Uric acid

25

Febuxostat is a selective inhibitor of xanthine oxidase, which is used to manage hyperuricemia in patients with gout. The objective of the study was to compare the pharmacokinetics of two different strength of febuxostat formulations (80 mg and 40 mg).

Concepts: Hypouricemia, Xanthine, Hyperuricemia, Xanthine oxidase, Xanthine oxidase inhibitor, Gout, Uric acid

24

Since uric acid is associated with cardiovascular and renal disease, a treatment to maintain blood uric acid level may be required in patients with hyperuricemia. This study aims to evaluate preventive effects of febuxostat, a selective xanthine oxidase inhibitor, on cerebral, cardiovascular, and renal events in patients with hyperuricemia compared to conventional treatment.

Concepts: Kidney stone, Urine, Xanthine, Hyperuricemia, Xanthine oxidase, Xanthine oxidase inhibitor, Gout, Uric acid

23

Several epidemiological studies have demonstrated the existence of a correlation between high serum uric acid (SUA) levels, hypertension, and chronic kidney disease (CKD). Xantine oxidase inhibitors (XOI) are the most powerful uric acid lowering drugs, with presumed beneficial effects on cardiovascular and renal system. The multifactorial mechanism linking hyperuricemia with cardiovascular and renal diseases involves both the SUA level and the xanthine oxidase (XO) activity. In this context, the clinical research has been recently focused at assessing the efficacy of urate-lowering drugs active on XO in patients with abnormal blood pressure values and renal dysfunction. The mechanism of action responsible for the beneficial effect of XOI has not completely elucidated, and long-term studies involving large population samples are needed. In particular, XOI could play an important role in the management of hypertension and CKD, especially in patients not entirely controlled by conventional therapies. In the present review, we summarize the results of recent clinical trials that largely support a positive effect of allopurinol and febuxostat on blood pressure, glomerular filtration rate (GFR), and serum creatinine in different populations of patients. Will these drugs be considered a reliable choice or alternative to currently used drugs for the hypertension and kidney failure treatment? The debate is open, but much evidence is accumulating and supporting this role.

Concepts: Electrolyte, Uric acid, Xanthine oxidase, Renal physiology, Kidney, Renal failure, Nephrology, Chronic kidney disease

8

Lesinurad is an oral inhibitor of the monocarboxylic/urate transporter URAT1 encoded by the SLC22A12 gene. Market authorization was granted in February 2016 in Europe and December 2015 in the USA. As a potentially nephrotoxic uricosuric drug acting on the kidney, nephrologists should become familiar with its indications and safety profile. The approved indication is treatment of gout in combination with a xanthine oxidase (XO) inhibitor in adult patients who have not achieved target serum uric acid levels with an XO inhibitor alone. It is not indicated for asymptomatic hyperuricaemia or for patients with estimated creatinine clearance <45 mL/min. The only authorized daily dose is 200 mg and cannot be exceeded because of the nephrotoxicity risk. Nephrotoxicity is thought to be related to uricosuria. At the 200 mg/day dose, serum creatinine more than doubled in 1.8% of lesinurad patients (versus 0% in placebo) and in 11% of these it was not reversible. In addition, it is subject to a risk management plan given the potential association with cardiovascular events. In randomized clinical trials, the association of lesinurad with either allopurinol or febuxostat achieved a greater reduction in serum uric acid (∼1 mg/dL lower) than the XO inhibitors alone, and this allowed the serum uric acid target to be met in a higher proportion of patients, which was the primary endpoint. However, no clinical differences were observed in gout flares or tophi, although these were not the primary endpoints.

Concepts: Renal physiology, Xanthine oxidase inhibitor, Xanthine oxidase, Nephrology, Kidney stone, Hyperuricemia, Gout, Uric acid

1

Hyperuricemia is associated with hypertension, with elevated serum uric acid levels postulated to have a causal role in the development of hypertension. Consequently, serum uric acid reduction may help lower blood pressure (BP). A Phase 2, double-blind, placebo-controlled trial was conducted to assess the potential BP-lowering effects of the xanthine oxidase inhibitor febuxostat in subjects with hypertension and hyperuricemia (serum uric acid ≥0.42 mmol/L [≥7.0 mg/dL]).

Concepts: Stroke, Metabolic syndrome, Xanthine, Hyperuricemia, Xanthine oxidase, Xanthine oxidase inhibitor, Gout, Uric acid

1

Karapxa decoction (KD) is a Traditional Uighur Medicine used for hepatitis, cholecystitis, gastralgia, oedema, gout and arthralgia. Because of its purported effect in gout, its effects were tested in hyperuricemic mice models induced by yeast extract paste or potassium oxonate, as well as its capacity to scavenge free radicals in vitro.

Concepts: Gout, Fructose, Ammonia, Xanthine, Xanthine oxidase, Uric acid