In mammals, excess purine nucleosides are removed from the body by breakdown in the liver and excretion from the kidneys. Uric acid is the end product of purine metabolism in humans. Two-thirds of uric acid in the human body is normally excreted through the kidney, whereas one-third undergoes uricolysis (decomposition of uric acid) in the gut. Elevated serum uric acid levels result in gout and could be a risk factor for cardiovascular disease and diabetes. Recent studies have shown that human ATP-binding cassette transporter ABCG2 plays a role of renal excretion of uric acid. Two non-synonymous single nucleotide polymorphisms (SNPs), i.e., 421C>A (major) and 376C>T (minor), in the ABCG2 gene result in impaired transport activity, owing to ubiquitination-mediated proteosomal degradation and truncation of ABCG2, respectively. These genetic polymorphisms are associated with hyperuricemia and gout. Allele frequencies of those SNPs are significantly higher in Asian populations than they are in African and Caucasian populations. A rapid and isothermal genotyping method has been developed to detect the SNP 421C>A, where one drop of peripheral blood is sufficient for the detection. Development of simple genotyping methods would serve to improve prevention and early therapeutic intervention for high-risk individuals in personalized healthcare.

The aim of this work is to facilitate the nutritional therapy of gout and hyperuricemia. In Japan, patients with gout or hyperuricemia are recommended to consume less than 400 mg of dietary purines per day. When receiving nutritional therapy for gout or hyperuricemia, purine-rich foods (>200 mg/100 g) should be eaten in even lower quantities. The purine content of foods reported in this study are as follows: noodles, 0.6–12.1 mg/100 g; bread, 4.4 mg/100 g; peas or seeds, 19.6–67.1 mg/100 g; dairy, 0.0–1.4 mg/100 g; Japanese vegetables, 0.9–47.1 mg/100 g; seasonings, 0.7–847.1 mg/100 g; meat or fish, 19.0–385.4 mg/100 g; fish milt, 375.4–559.8 mg/100 g; and supplements, 81.9–516.0 mg/100 g. Foods containing very large amounts of purine (>300 mg/100 g) included anchovy, cutlassfish (hairtail), cod milt, globefish milt, dried Chinese soup stock, dried yeast, a Euglena supplement, and a Lactobacillus supplement. When eating these high-purine food or supplements, the quantity taken at one meal should be limited, especially milt because they typically consumed amount of 20–30 g is equivalent to 75–168 mg total purines. This is 20%–40% of the recommended daily amount (400 mg/day) for patients with gout or hyperuricemia. Thus, these patients should restrict the amount of purine-rich foods they consume. Good dietary habits with a good balance of nutrients are recommended.

Objectives:  To analyze the crystal components and matrix proteins of urinary stones by proteomic analysis using liquid chromatography–tandem mass spectrometry.Methods:  Urinary stones were obtained from patients with gout and hyperuricemia. The outside and inside of the stones were measured non‐destructively with a micro area X‐ray diffractometer. After stones were powdered, extracted proteins were analyzed by proteomic analysis.Results:  Of 17 investigated stones, seven were composed of calcium oxalate monohydrate or calcium oxalate dihydrate, seven were of uric acid, and three were a mixture of calcium oxalate monohydrate and uric acid. In calcium oxalate monohydrate or calcium oxalate dihydrate stones, osteopontin, uromodulin, albumin, protein Z, prothrombin, protein S, hemoglobin and histone H4 were identified. In uric acid stones, uromodulin, albumin, hemoglobin, calgranulins and immunoglobin G fragments were detected. Mixed stones of calcium oxalate monohydrate and uric acid contained both Ca‐binding proteins and abundant proteins. Matrix proteins were different when the crystal components of the stone were different, even when from the same patient.Conclusions:  Proteins, such as uromodulin and albumin, are often detected in stones, regardless of crystal components. However, osteopontin, prothrombin, protein S and protein Z are identified specifically in calcium oxalate stones. Furthermore, immunoglobin G fragments are detected in uric acid stones. The role of these specific proteins in the different types of stones can be of particular interest.

Purine contents of soybean-derived food and various other Japanese foods were quantitatively determined by high-performance liquid chromatography (HPLC). Purine contents were as follows: soybean-derived foods, 21.9–172.5 mg/100 g or 100 mL; Japanese vegetables, 2.3–171.8 mg/100 g; Japanese mushrooms, 9.5–142.3 mg/100 g. Since purine levels in these foods did not exceed 200 mg/100 g, we recommend that eating of them should be adopted and good dietary habits followed.