Analysis of Intra- and Extracellular Levels of Purine Bases, Nucleosides, and Nucleotides in HepG2 Cells by High-performance Liquid Chromatography

Exploring Dynamic Metabolome of the HepG2 Cell Line: Rise and Fall

Both biological and technical variations can discredit the reliability of obtained data in omics studies. In this technical note, we investigated the effect of prolonged cultivation of the HepG2 hepatoma cell line on its metabolomic profile. Using the GC × GC-MS approach, we determined the degree of metabolic variability across HepG2 cells cultured in uniform conditions for 0, 5, 10, 15, and 20 days. Post-processing of obtained data revealed substantial changes in relative abundances of 110 metabolites among HepG2 samples under investigation. Our findings have implications for interpreting metabolomic results obtained from immortal cells, especially in longitudinal studies. There are still plenty of unanswered questions regarding metabolomics variability and many potential areas for future targeted and panoramic research. However, we suggest that the metabolome of cell lines is unstable and may undergo significant transformation over time, even if the culture conditions remain the same. Considering metabolomics variability on a relatively long-term basis, careful experimentation with particular attention to control samples is required to ensure reproducibility and relevance of the research results when testing both fundamentally and practically significant hypotheses.

Determination of total purine and free purine content in milk, soymilk, and enteral nutritional supplements to assist nutritional therapy for hyperuricemia and gout

In this study, we determined the purine contents in milk and soymilk, as protein-rich drinks, and in enteral nutritional supplements employed to ameliorate protein malnutrition in the elderly. Milk consumption is known to lower serum uric acid levels and to promote uric acid excretion. However, discrepant results have been reported regarding the effect of soymilk on serum uric acid levels. The purpose of this study was to quantify and compare the total purine contents and the contents of individual purines and pyrimidines by molecular type (nucleotides, nucleosides, and bases).

Biosynthesis of allantoin in Escherichia coli via screening a highly effective urate oxidase

Allantoin is an important fine chemical that can be widely used in pharmaceutical, cosmetic and agricultural industries. Currently, allantoin is mainly produced by plant extraction or chemical synthesis. Due to the cost and environmental concerns, biosynthesis of allantoin from renewable feedstock is much more desirable. However, microbial production of allantoin from simple carbon sources has not yet been achieved so far. In this work, de novo biosynthesis of allantoin was achieved by constructing an artificial biosynthetic pathway. First, screening of efficient urate oxidases and xanthine dehydrogenases enabled allantoin production from hypoxanthine, a natural intermediate in purine metabolic pathway in E. coli. Then, assemble of the entire pathway resulted in 13.9 mg/L allantoin from glucose in shake flask experiments. The titer was further improved to 639.8 mg/L by enhancing the supply of the precursor, redistribution of carbon flux, and reduction of acetate. Finally, scale-up production of allantoin was conducted in a 1-L fermentor under fed-batch culture conditions, which enabled the synthesis of 2360 mg/L allantoin, representing a 170-fold increase compared with the initial strain. This work not only demonstrates the potential for industrial production of allantoin, but also provides a bacterial platform for synthesis of other purines-derived high value chemicals. This article is protected by copyright. All rights reserved.

Xanthinuria Type 1 with a Novel Mutation in Xanthine Dehydrogenase and a Normal Endothelial Function

Whether or not extremely low levels of serum uric acid (SUA) in xanthinuria are associated with impairment of the endothelial function and exercise-induced acute kidney injury (EIAKI) is unclear. A 59-year-old woman without EIAKI or urolithiasis had undetectable levels of UA in serum and urine and elevated levels of hypoxanthine and xanthine in urine. A genetic analysis revealed homozygous mutations in the XDH gene [c.1585 C>T (p. Gln529*)]. Flow-mediated dilation was within the normal range. This is the first report of a case with extremely low levels of SUA, xanthinuria with novel mutations of xanthine dehydrogenase (XDH) and a normal endothelial function.

Measurement of the total purine contents and free nucleosides, nucleotides, and purine bases composition in Japanese anchovies (Engraulis japonicus) using high-performance liquid chromatography with UV detection

Dietary purine restrictions are recommended for patients with hyperuricemia and gout. While measuring the purine contents of various foods in our laboratory using high-performance liquid chromatography (HPLC), we observed and reported changes in purine composition. In this study, we measured the total purine content and free purine of raw anchovies as well as after fermentation, using two methods by HPLC. Method 1 involved acid hydrolysis of all purines, such as nucleic acids and nucleotides, to form four corresponding purine bases. Method 2, which is a non-hydrolysis method, is used to measure the amount of free purines (nucleotide, nucleoside, purine base). As a result of method 1, after fermentation, adenine-related and hypoxanthine-related purines and the total purine levels decreased significantly. Regardless of being raw or fermented, each anchovy contained mainly hypoxanthine- and guanine-related purines. Among the hypoxanthine-related purines, the results of method 2 revealed that the raw anchovies contained a lot of inosine monophosphate (IMP), while after fermentation contained more inosine. In guanine-related and adenine-related purines, those nucleotides decreased by fermentation and nucleosides and bases increased. Measurements of free purines revealed that those reductions after fermentation observed in method 1 were derived from decreased nucleotides. These results indicate that purines are affected by the fermentation bacteria and period.

Effects of islatravir (4'-ethynyl-2-fluoro-2'-deoxyadenosine or EFdA) on renal tubular cells and islatravir's interactions with organic anion transporters

Islatravir (ISL; 4'-ethynyl-2-fluoro-2'-deoxyadenosine or EFdA) is a novel reverse transcriptase translocation inhibitor and has a unique structure and high antiviral activity against wild-type and multidrug resistant HIV strains. In this study, we investigated whether islatravir (ISL) can cause kidney damage compared to tenofovir disoproxil fumarate (TDF) and tenofovir (TFV). We also investigated interactions of these drugs with organic anion transporters (OATs). There is a large gap in ISL concentration between the pharmacological dose to proximal tubular cells and the clinical dose. ISL is unlikely to be taken up via OAT1 or OAT3; therefore, OAT1 and OAT3 may not be involved in the injury to tubular cells. Present data strongly suggests that ISL is not toxic to proximal tubules because blood levels of ISL are not high enough to cause kidney damage in the clinical setting.

Improved Parkinsons disease motor score in a single-arm open-label trial of febuxostat and inosine

BACKGROUND

Cellular energetics play an important role in Parkinsons disease etiology, but no treatments directly address this deficiency. Our past research showed that treatment with febuxostat and inosine increased blood hypoxanthine and ATP in healthy adults, and a preliminary trial in 3 Parkinson's disease patients suggested some symptomatic improvements with no adverse effects.

METHODS

To examine the efficacy on symptoms and safety in a larger group of Parkinsons disease patients, we conducted a single-arm, open-label trial at 5 Japanese neurology clinics and enrolled thirty patients (nmales = 11; nfemales = 19); 26 patients completed the study (nmales = 10; nfemales = 16). Each patient was administered febuxostat 20 mg and inosine 500 mg twice-per-day (after breakfast and dinner) for 8 weeks. The primary endpoint was the difference of MDS-UPDRS Part III score immediately before and after 57 days of treatment.

RESULTS

Serum hypoxanthine concentrations were raised significantly after treatment (Pre = 11.4 μM; Post = 38.1 μM; P < .0001). MDS-UPDRS Part III score was significantly lower after treatment (Pre = 28.1 ± 9.3; Post = 24.7 ± 10.8; mean ± SD; P = .0146). Sixteen adverse events occurred in 13/29 (44.8%) patients, including 1 serious adverse event (fracture of the second lumbar vertebra) that was considered not related to the treatment.

CONCLUSIONS

The results of this study suggest that co-administration of febuxostat and inosine is relatively safe and effective for improving symptoms of Parkinsons disease patients. Further controlled trials need to be performed to confirm the symptomatic improvement and to examine the disease-modifying effect in long-term trials.

Simultaneous quantification of 8 nucleotides and adenosine in cells and their medium using UHPLC-HRMS

Purinergic signalling is involved in physiological processes, particularly during ischemia-reperfusion injuries for which it has a protective effect. The purpose of this work was to develop a method for simultaneous quantification of eight nucleotides and adenosine in biological matrices by liquid chromatography coupled with high-resolution mass spectrometry. A method was developed that was sufficiently robust to quantify the targeted analytes in 20 min with good sensitivity. Analysis of extracellular media from cultured endothelial cells detected the release of nucleotides and adenosine during 2 h of hypoxia. The quantification of cylic adenosine monophosphate (cAMP) allowed to establish a dose-response curve after receptor stimulation. Therefore, our method allows us to study the involvement of nucleotides in various processes in both the intracellular and extracellular compartment.

The observed variation in the purine composition of food after soaking in sake lees

In this study, we investigated the alterations in the purine composition of swordfish prepared using a traditional Japanese processing method of soaking in sake lees. These alterations are the byproducts of the yeast fermentation of rice-koji and are renowned for enhancing the umami nature of food. Using a conventional assay method for hydrolyzing all of the purines into four bases and our developed method for simultaneously analyzing purines, we observed the alterations in four purine bases in the soaked sake lees and swordfish. The findings showed that the total purine content, and hypoxanthine-related and guanine-related purines in swordfish decreased after soaking in sake lees. We also analyzed the free purine composition and showed that the ratio of IMP in swordfish was decreased by soaking, while that of inosine in sake lees was increased by soaking swordfish in it.

Simultaneous quantification by HPLC of purines in umami soup stock and evaluation of their effects on extracellular and intracellular purine metabolism

Ribonucleotide flavor enhancers such as inosine monophosphate (IMP) and guanosine monophosphate (GMP) provide umami taste, similarly to glutamine. Japanese cuisine frequently uses soup stocks containing these nucleotides to enhance umami. We quantified 18 types of purines (nucleotides, nucleosides, and purine bases) in three soup stocks (chicken, consommé, and dried bonito soup). IMP was the most abundant purine in all umami soup stocks, followed by hypoxanthine, inosine, and GMP. The IMP content of dried bonito soup was the highest of the three soup stocks. We also evaluated the effects of these purines on extracellular and intracellular purine metabolism in HepG2 cells after adding each umami soup stock to the cells. An increase in inosine and hypoxanthine was evident 1 h and 4 h after soup stock addition, and a low amount of xanthine and guanosine was observed in the extracellular medium. The addition of chicken soup stock resulted in increased intracellular and extracellular levels of uric acid and guanosine. Purine metabolism may be affected by ingredients present in soups.

Evaluation of cellular purine transport and metabolism in the Caco-2 cell using comprehensive high-performance liquid chromatography method for analysis of purines

Using Caco-2 cells and our previously developed high-performance liquid chromatography method for quantification of purine bases, nucleosides, and nucleotides, we evaluated cellular purine transport and uptake. The analytes were separated using YMC-Triart C18 column with gradient elution. We used Caco-2 cells as intestinal model cells and monitored purine transport across a monolayer for 2 h. The degree of change of purine concentrations in the permeate was very slight; however, it was possible to simultaneously determine these parameters for all purines because of our method's high sensitivity. In the present study, the purine bases (adenine, guanine, hypoxanthine, and xanthine) showed a relatively high permeability as compared with the nucleosides (adenosine, guanosine, inosine, and xanthosine). Increased concentration of metabolites in the permeate was also observed following the addition of purines. In a cell uptake assay, both the cell culture medium (extracellular) and the cells extracted from Caco-2 with acetonitrile:water (7:3) (intracellular) were measured. The additional nucleoside did not increase significantly within the cells. On the other hand, we observed that nucleotide, such as ATP, increased in the cell in a time-dependent manner following the addition of nucleoside. The additional nucleosides were considered to be rather recycled via the salvage pathway than metabolized to purine bases and/or uric acid in the cell. Such differences might have affected the increase in the serum uric acid levels depending on purine form.