A Novel Multi-Epitope Vaccine Based on Urate Transporter 1 Alleviates Streptozotocin-Induced Diabetes by Producing Anti-URAT1 Antibody and an Immunomodulatory Effect in C57BL/6J Mice

The dysregulation of immune cells induced by uric acid: mechanisms of inflammation associated with hyperuricemia and its complications

Changes in lifestyle induce an increase in patients with hyperuricemia (HUA), leading to gout, gouty arthritis, renal damage, and cardiovascular injury. There is a strong inflammatory response in the process of HUA, while dysregulation of immune cells, including monocytes, macrophages, and T cells, plays a crucial role in the inflammatory response. Recent studies have indicated that urate has a direct impact on immune cell populations, changes in cytokine expression, modifications in chemotaxis and differentiation, and the provocation of immune cells by intrinsic cells to cause the aforementioned conditions. Here we conducted a detailed review of the relationship among uric acid, immune response, and inflammatory status in hyperuricemia and its complications, providing new therapeutic targets and strategies.

Short Hexapeptide Optimized from Rice-Derived Peptide 1 Shows Promising Anti-hyperuricemia Activities

Plant-derived peptides are a treasure trove for new-generation anti-hyperuricemia drugs. In the current study, we optimized a short hexapeptide rice-derived peptide 1 (RDP1)-M3 (AAAAGA) according to the anti-hyperuricemia RDP1 peptide identified from rice in our previous research. Results showed that RDP1-M3 exerted better hyperuricemia-alleviating and xanthine oxidase (XOD)-inhibiting potency in mice than RDP1. The biodistribution of RDP1-M3 was also analyzed. RDP1-M3 directly decreased XOD and uric acid levels in vivo and in vitro. In addition, RDP1-M3 reduced the expression of urate transporter 1 and glucose transporter 9, increased the level of organic anion transporter 1, reduced the expression of NOD-like receptor superfamily pyrin 3 inflammasomes, and reduced the levels of interleukin-1β and tumor necrosis factor-α of hyperuricemic mice. Thus, our results indicated that the optimized short hexapeptide RDP1-M3 may be a candidate drug for anti-hyperuricemia.

Discovery of a novel rice-derived peptide with significant anti-gout potency

As a metabolic disease, gout, which seriously affects the normal life of patients, has become increasingly common in modern society. However, the existing medicines cannot completely meet the clinical needs. In the current study, a novel short peptide (named rice-derived-peptide-2 (RDP2), AAAAGAMPK-NH2, 785.97 Da) was isolated and identified from water extract of shelled Oryza sativa fruits, without toxic side effects but excellent stability. Our results indicated that RDP2 (the minimum effective concentration is 5 μg kg^-1) induced a significant reduction in serum uric acid levels in hyperuricemic mice via suppressing xanthine oxidase activity and urate transporter 1 expression, as well as alleviated renal damage through inhibiting the activation of NLRP3 inflammasome. In addition, RDP2 can also alleviate paw swelling and inflammatory reactions in mice after subcutaneous injection of monosodium urate crystals. As mentioned above, we obtained a novel peptide which could work through all stages of gout, not only reducing uric acid levels and renal damage in hyperuricemic mice, but also alleviating inflammatory responses associated with acute gout attack, and thus provided a new peptide molecular template for the development of anti-gout drugs.

Hypouricemic and nephroprotective roles of anthocyanins in hyperuricemic mice

Hyperuricemia (HUA) is a universal metabolic disorder characterized by a high level of uric acid in the serum. Anthocyanins (ACNs) are a group of natural flavonoids that have shown favourable bioactivities in the metabolic syndrome but the effect on uric acid metabolism remains underexplored. The present study investigated the hypouricemic effects of ACNs in a mice model and further studied the potential mechanisms. ICR mice based on a high-yeast diet were administered potassium oxonate (PO, 280 mg per kg body weight) and inosine (400 mg per kg body weight) to induce a hyperuricemia model, meanwhile, ACNs were supplemented by gavage. The mice were sacrificed after 3 weeks of treatment. ACN administration significantly reduced serum uric acid (SUA), blood urea nitrogen (BUN) and serum creatinine (Scr) levels and suppressed xanthine oxidase (XOD) activity in mice serum and liver. In addition, ACNs down-regulated the expression of hepatic XOD, caspase-1, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) and regulated the expression of renal urate transporters URAT1, GLUT9, ABCG2, OAT1, OAT3, OCT1, OCT2, OCTN1 and OCTN2. According to histological analysis, ACN treatment exhibited hepatoprotective and nephroprotective effects in hyperuricemic mice. In conclusion, ACNs reduced urate production and promoted uric acid excretion from the renal system, which suggests the potential of ACNs for the future treatment of HUA.

The Proposal of Molecular Mechanisms of Weak Organic Acids Intake-Induced Improvement of Insulin Resistance in Diabetes Mellitus via Elevation of Interstitial Fluid pH

Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35~7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: (1) the carboxyl group (R-COO⁻) but not H⁺ composing weak organic acids in foods is absorbed into the body, and (2) the absorbed the carboxyl group (R-COO⁻) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus; however, the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H⁺ associated with ATP synthesis required for the Na⁺,K⁺-ATPase to extrude the high leveled intracellular Na⁺ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.