| Gout, suffered as a chronic life-long disease, is a series of purine metabolic disorders which commonly happened in humans. It is characterized by marked hyperuricemia in which serum uric acid was elevated by either the production increase or excretion decrease of uric acid. Given the high rate of incidence, recurrence and being more and more serious hazardness of gout, studies on the prevention and treatment of gout as well as hyperuricemia are of important theoretical and clinical significance.Ramulus Mori is the twigs of Morus alba L. which belongs to Moraceae family. As a traditional Chinese medicine, ramulus Mori has been collected by Chinese pharmacopoeia and used clinically to treat a group of diseases related to gout, such as rheumatism, joint inflammation, numbness of hands and feet, and paralysis. Though many researches on the pharmacological activities and chemical constituents of ramulus Mori have been reported, especially those on the flavonoids and their pharmacological activities. However, the research on the treatment of hyperuricemia of ramulus Mori extract and its major constituents were seldom. The present study investigated the hypouricemic effects and mechanisms of ramulus Mori ethanol extract on the animal model of hyperuricemia. Major constituents of ramulus Mori extract were also isolated by systematic extractions and isolations. The hypouricemic effects and mechanisms of its major constituents were also been investigated. The results could provide novel scientific basis for the clinical application of this traditional Chinese medicine. Therefore, to clarify the hypouricemic effects of the ramulus Mori extract and its main constituents, the present study had accomplished relevant researches as follows.1. On the potassium oxonate-induced hyperuricemic model of mice, ramulus Mori extract was comfirmed to reduce uric acid levels in mouse serum and liver by inhibiting hepatic XOD activity and its mRNA and protein expressions, meanwhile reducing renal mURAT1mRNA and protein expressions. These results indicated that ramulus Mori extract exhibited its hypouricemic effect by both inhibiting uric acid formation and promoting its renal excretion.2. From the ethanol extract of ramulus Mori,26chemical constituents were isolated by various chromatographic methods. On the basis of spectroscopic analysis (1D-NMR,2D-NMR, MS),20of them were identified as stilbenes, flavonoids, phenolic and steroid compounds.The20identified compounds included2Stilbene compounds as mulberroside A and oxyresveratrol. Another14flavonoids are respectively quercetin, kaempferol, luteolin, cudraflavone C, steppogenin, norartocarpetin, morachalcone A, butein, isoquercetin, hyperin, quercetin-3-O-β-D-mannanpyranosid, rubraflavone A, kaempferol3-β-D-glucoside and naringenine. The2phenolic compounds are trans-4-hydroxycinnamic acid and moracin M. The2steroid compounds are P-sidosterol and daucosterol.3. By analyzing the structures of the20compounds and previous related researches in our laboratory, mulberroside A was selected to study its uricosuric effect. On the protassium oxonate-induced hyperuricemia model of mice, mulberroside A significantly reduced the uric acid levels in serum and liver, elevated urinary uric acid levels and fraction urate clearance (FEua) of hyperuricemic mice. These results demonstrated that mulberroside A promoted renal urate secretion of hyperuricemic mice.RT-PCR and western blotting were applied to study the effects of mulberroside A on renal urate related organic anion transporters of hyperuricemic mice. Mulberroside A down-regulated mRNA and protein expressions of urate transporter1(mURAT1) and glucose transporter9(mGLUT9), while up-regulated mRNA and protein expressions of organic anion transporter1(mOAT1) in mouse kidney. The results revealed that the hypouricemic effect of mulberroside A could attribute to its promotion of urate excretion by inhibiting renal urate reabsorption and increasing renal urate secretion of hyperuricemic mice.Moreover, the present study reported the up-regulation of mulberroside A on mRNA and protein expressions of renal organic cation transporter1and2(mOCT1and mOCT2), accompanying with decreased serum creatinine levels and elevated urine creatinine levels of hyperuricemic mice. These results indicated the protection of mulberroside A on the kidneys of hyperuricemic mice.Summarily speaking, ramulus Mori extract exhibited hypouricemic effect in hyperuricemic mice, from which20compounds was indentified as stilbenes, flavonoids, phenolic and steroid compounds. And mulberroside A was its main active component of this extracr. The present paper demonstrated that mulberroside A exhibited significant uricosuric effect in hyperuricemic mice by regulating the expressions of urate related organic anion transporters to inhibit renal urate reabsorption and promote urate secretion. Based on this mechanism, mulberroside A could improve the urate imbalance state of hyperuricemic mice. Additionally, mulberroside A exhibited kidney protection by up-regulating expressions of renal mOCT1and mOCT2in hyperuricemic mice. These results provided new scientific basis for the clinical usage of ramulus Mori in treatment of hyperuricemia and gout. |
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