Efficacy of pentosan polysulfate for the treatment of interstitial cystitis/bladder pain syndrome: results of a systematic review of randomized controlled trials.

Background: Among the numerous therapeutic approaches used in the treatment of interstitial cystitis/bladder pain syndrome (IC/BPS) few have been assessed with a sufficient level of evidence. The safety and efficacy of pentosan polysulfate sodium (PPS) has been shown in several open-label and comparative clinical trials with different populations including two meta-analyses. In the context of the approval procedure of PPS for the treatment of IC/BPS by the European Medicines Agency we updated the findings of the previous analyses by incorporating the results of the latest studies.Method: Relevant studies based on a systematic review of PubMed/Medline and the Cochrane Library in June 2018 were identified. For completeness control, clinical trial registries were also searched. Only randomized, placebo-controlled clinical trials providing sufficient information to estimate at least one relevant effect size measure to compare the efficacy of PPS versus placebo were included in the analysis.Results: Of the studies identified in the literature search, six randomized placebo-controlled studies met the pre-defined eligibility criteria. Analyses showed no indication of heterogeneity or publication bias. Treatment with PPS led to a statistically significant improvement in the patient's overall response assessment (p < .001), pain (p = .009) and urgency (p = .005).Conclusions: Our meta-analyses confirmed the results of preceding meta-analyses showing that PPS is efficacious compared to placebo in the treatment of bladder pain, urinary urgency and frequency of micturition and thus an evident option for the treatment of IC/BPS symptoms.

The crystal structures of Zea mays and Arabidopsis 4-hydroxyphenylpyruvate dioxygenase.

The transformation of 4-hydroxyphenylpyruvate to homogentisate, catalyzed by 4-hydroxyphenylpyruvate dioxygenase (HPPD), plays an important role in degrading aromatic amino acids. As the reaction product homogentisate serves as aromatic precursor for prenylquinone synthesis in plants, the enzyme is an interesting target for herbicides. In this study we report the first x-ray structures of the plant HPPDs of Zea mays and Arabidopsis in their substrate-free form at 2.0 A and 3.0 A resolution, respectively. Previous biochemical characterizations have demonstrated that eukaryotic enzymes behave as homodimers in contrast to prokaryotic HPPDs, which are homotetramers. Plant and bacterial enzymes share the overall fold but use orthogonal surfaces for oligomerization. In addition, comparison of both structures provides direct evidence that the C-terminal helix gates substrate access to the active site around a nonheme ferrous iron center. In the Z. mays HPPD structure this helix packs into the active site, sequestering it completely from the solvent. In contrast, in the Arabidopsis structure this helix tilted by about 60 degrees into the solvent and leaves the active site fully accessible. By elucidating the structure of plant HPPD enzymes we aim to provide a structural basis for the development of new herbicides.

Structure and properties of an engineered transketolase from maize.

The gene specifying plastid transketolase (TK) of maize (Zea mays) was cloned from a cDNA library by southern blotting using a heterologous probe from sorghum (Sorghum bicolor). A recombinant fusion protein comprising thioredoxin of Escherichia coli and mature TK of maize was expressed at a high level in E. coli and cleaved with thrombin, affording plastid TK. The protein in complex with thiamine pyrophoshate was crystallized, and its structure was solved by molecular replacement. The enzyme is a C2 symmetric homodimer closely similar to the enzyme from yeast (Saccharomyces cerevisiae). Each subunit is folded into three domains. The two topologically equivalent active sites are located in the subunit interface region and resemble those of the yeast enzyme.

Biosynthesis of pteridines. Reaction mechanism of GTP cyclohydrolase I.

GTP cyclohydrolase I catalyses the hydrolytic release of formate from GTP followed by cyclization to dihydroneopterin triphosphate. The enzymes from bacteria and animals are homodecamers containing one zinc ion per subunit. Replacement of Cys110, Cys181, His112 or His113 of the enzyme from Escherichia coli by serine affords catalytically inactive mutant proteins with reduced capacity to bind zinc. These mutant proteins are unable to convert GTP or the committed reaction intermediate, 2-amino-5-formylamino-6-(beta-ribosylamino)-4(3H)-pyrimidinone 5'-triphosphate, to dihydroneopterin triphosphate. The crystal structures of GTP complexes of the His113Ser, His112Ser and Cys181Ser mutant proteins determined at resolutions of 2.5A, 2.8A and 3.2A, respectively, revealed the conformation of substrate GTP in the active site cavity. The carboxylic group of the highly conserved residue Glu152 anchors the substrate GTP, by hydrogen bonding to N-3 and to the position 2 amino group. Several basic amino acid residues interact with the triphosphate moiety of the substrate. The structure of the His112Ser mutant in complex with an undefined mixture of nucleotides determined at a resolution of 2.1A afforded additional details of the peptide folding. Comparison between the wild-type and mutant enzyme structures indicates that the catalytically active zinc ion is directly coordinated to Cys110, Cys181 and His113. Moreover, the zinc ion is complexed to a water molecule, which is in close hydrogen bond contact to His112. In close analogy to zinc proteases, the zinc-coordinated water molecule is suggested to attack C-8 of the substrate affording a zinc-bound 8R hydrate of GTP. Opening of the hydrated imidazole ring affords a formamide derivative, which remains coordinated to zinc. The subsequent hydrolysis of the formamide motif has an absolute requirement for zinc ion catalysis. The hydrolysis of the formamide bond shows close mechanistic similarity with peptide hydrolysis by zinc proteases.

Reaction mechanism of GTP cyclohydrolase I: single turnover experiments using a kinetically competent reaction intermediate.

GTP cyclohydrolase I catalyses the transformation of GTP into dihydroneopterin 3'-triphosphate, which is the first committed precursor of tetrahydrofolate and tetrahydrobiopterin. The kinetically competent reaction intermediate, 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone, was used as substrate for single turnover experiments monitored by multiwavelength photometry. The early reaction phase is characterized by the rapid appearance of an optical transient with an absorption maximum centred at 320. This species is likely to represent a Schiff base intermediate at the initial stage of the Amadori rearrangement of the carbohydrate side-chain. Deconvolution of the optical spectra suggested four linearly independent processes. A fifth reaction step was attributed to photodecomposition of the enzyme product. Pre-steady state experiments were also performed with the H179A mutant which can catalyse a reversible conversion of GTP to 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone but is unable to form the final product, dihydroneopterin triphosphate. Optical spectroscopy failed to detect any intermediate in the reversible reaction sequence catalysed by the mutant protein. The data obtained with the wild-type and mutant protein in conjunction with earlier quenched flow studies show that the enzyme-catalysed opening of the imidazole ring of GTP and the hydrolytic release of formate from the resulting formamide type intermediate are both rapid reactions by comparison with the subsequent rearrangement of the carbohydrate side-chain which precedes the formation of the dihydropyrazine ring of dihydroneopterin triphosphate.