Dual Effects Of Pyrazinoate On Urate Transport

The anti-uricosuric agent pyrazinoate (PZA), a metabolite of pyrazinamide, has dual effects on urate transport by the proximal tubule. Urate uptake by brush-border membrane vesicles isolated from canine kidney cortex is shown, in the presence of 100 mM sodium (Na+) with 0.1 mM PZA, 0 PZA, or 5 mM PZA. The concentration results in Na+-dependent uptake of PZA and a potentiation of urate uptake via urate transporter-1 (URAT1); in contrast, the higher concentration cis-inhibits URAT1, thus reducing urate uptake by the membrane vesicles. (Reproduced with permission from reference 93: Guggino SE, Aronson PS. Paradoxical effects of pyrazinoate and nicotinate on urate transport in dog renal microvillus membranes. J Clin Invest. 1985;76:543-7.)

Chart showing how low concentrations of pyrazinoate stimulate uric acid to be reabsorbed, whereas higher concentrations reduce re-absorption.

Dual Effects Of Pyrazinoate On Urate Transport

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Urate Transport Mechanisms In Kidney

Urate transporter-1 (URAT1) is located in the apical membrane of proximal tubular cells in human kidneys and transports urate from lumen to proximal tubular cells in exchange for anions in order to maintain electrical balance. This exchanger is essential for proximal tubular reabsorption of urate and is targeted by both uricosuric and antiuricosuric agents. Sodium-dependent entry of monovalent anions (such as pyrazinoate, nicotinate, lactate, pyruvate, β-hydroxybutyrate, and acetoacetate), presumptively through the sodium–anion cotransporter, fuels the absorption of luminal urate via the anion exchanger URAT1. Basolateral entry of urate during urate secretion by the proximal tubule is stimulated by sodium-dependent uptake of the divalent anion α-ketoglutarate, leading to urate-α-ketoglutarate exchange via organic anion transporter-1 (OAT1) or organic anion transporter-3 (OAT3). These proteins or similar transporters may facilitate the basolateral in?ux or efflux of urate. As discussed in the text, although the quantitative role of human urate secretion remains unclear, several molecular candidates have been proposed for the electrogenic urate secretion pathway in apical membrane of proximal tubules, including URAT1, ATP-driven ef?ux pathway (MRP4), and voltage-driven organic anion transporter-1 (OATV1). FEu = renal clearance of urate/glomerular ?ltration rate.

Diagram showing the effects of various substances on the re-absorption or clearance of urate within the kidney.

Urate Transport Mechanisms In Kidney

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Urate Production Pathways

The de novo synthesis starts with 5’-phosphoribosyl 1-pyrophosphate (PRPP), which is produced by addition of a further phosphate group from adenosine triphosphate (ATP) to the modi?ed sugar ribose-5-phosphate. This step is performed by the family of PRPP synthetase (PRS) enzymes. In addition, purine bases derived from tissue nucleic acids are reutilized through the salvage pathway. The enzyme hypoxanthine– guanine phosphoribosyl transferase (HPRT) salvages hypoxanthine to inosine monophosphate (IMP) and guanine to guanosine monophosphate (GMP). Only a small proportion of patients with urate overproduction have the well-characterized inborn errors of metabolism, such as superactivity of PRS and de?ciency of HPRT. Furthermore, conditions associated with net ATP degradation lead to the accumulation of adenosine diphosphate (ADP) and adenosine monophosphate (AMP), which can be rapidly degraded to uric acid. These conditions are displayed in left upper corner. Plus sign denotes stimulation, and minus sign denotes inhibition. APRT adenine phosphoribosyl transferase; PNP purine nucleotide phosphorylase.

Diagram showing some of the genetic and external influences on the stimulation or inhibition of internal synthesiis of uric acid

Urate Production Pathways

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40 30 30 Gout Diet

40 30 30 Gout Diet

Ann Rheum Dis. 2000 Jul;59(7):539-43.

Beneficial effects of weight loss associated with moderate calorie/carbohydrate restriction, and increased proportional intake of protein and unsaturated fat on serum urate and lipoprotein levels in gout: a pilot study.

Dessein PH, Shipton EA, Stanwix AE, Joffe BI, Ramokgadi J.

This report shows useful, though limited, blood uric acid reduction on a calorie controlled diet where nutrition is balanced to a 40:30:30 carbohydrate:protein:fats ratio.

To put this information in context, please see the Gout Diet Section.

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Fasturtec

Fasturtec

Product information for Fasturtec a brandname for rasburicase sold as Elitek in the USA. Contains interesting tables of outstanding uric acid reduction.

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Serum Urate And Recurrent Gout Attacks

Serum Urate And Recurrent Gout Attacks

A retrospective study of the relationship between serum urate level and recurrent attacks of gouty arthritis: evidence for reduction of recurrent gouty arthritis with antihyperuricemic therapy. Jun 2004. Shoji A et al. Gout study showing the relationship between persistent reduction of blood uric acid below the saturation point, and the reduction in frequency of acute gouty attacks.

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Treatment Failure Gout

Treatment Failure Gout

Treatment failure gout. Nov 2009 Ali S, Lally EV. Describes some potential treatment options in refractory (unresponsive) gout. Reasons for treatment failure are:

  1. Physician failure to diagnose and treat gout
  2. Inadequate dosing of urate-lowering therapy
  3. Allergy or intolerance to urate-lowering therapy
  4. Allergy or intolerance to urate-lowering therapy
  5. Lack of compliance with prescribed therapy

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