Mechanistic study of the effect of lactobacillus rhamnosus fermented soymilk on the progression of DOCA-salt induced hypertensive rats

Abstract

Hypertension, a modern metabolic syndrome, is a risk factor for many diseases such as stroke, myocardial infarction, congestive heart failure, and end-stage renal disease. Many drugs and food including captopril, benzothiadiazides, grapefruit and mulberry were found to decrease blood pressure or prevent hypertension. Soymilk is known to offer benefits for consumers as it contains many bioactive substances, like isoflavones. Lactic acid bacteria (LAB) could effectively transform glycoside form of isoflavones into aglycone form, which is readily absorbed and more bioavailable than other forms. Nineteen strains of LAB, including Lactobacillus and Leuconostoc, from different samples including kimchi, yogurt and baby feces were tested in our study. The isolated L.rhamnosus strain, S1, generally had an overall good performance on acid, salt and pathogens tolerance. Importantly, it showed best fermentation characteristics in soymilk, especially higher aglycones content and antioxidant ability in vitro over the other tested strains, demonstrating its potential for the further study in hypertensive animals. To build the hypertensive animal model, captopril, an angiotensin converting enzyme (ACE) inhibitor, was used in DOCA-salt hypertensive rats as a positive control to monitor if the DOCA-salt-induced hypertension could be restored by this drug. In our study, captopril was further proved to lower blood pressure, improve biochemical parameters and attenuate hypertrophy of both kidney and heart. By 16s rRNA sequencing, alterations of bacteria in gut microbiota were also evaluated. Escherichia-Shigella, Eubacteriumnodatum and Ruminococcus_2, rich in hypertensive rats, were able to be rebalanced by captopril. Bifidobacterium and Akkermansia were abundant in hypertensive rats treated with captopril. The predicted molecular functions of gut microbiota indicated the abundance of some bacteria involved in amino acids metabolism were able to be rebalanced by captopril in the hypertensive rats. Altogether, captopril improved the high blood pressure in DOCA-salt hypertensive rats via changing biochemical parameters and gut microbiota. Additionally, the water extract (WE) and ethanol extract (EE) of S1-fermented soymilk showed high antioxidant abilities in vitro. They also had protective effects on differentiated PC-12 and SH-SY5Y cells under H2O2 induced oxidative stress by increasing cell viability and reducing ROS generation. Furthermore, changes of blood pressure and gut microbiota in DOCA-salt hypertensive rats were observed by administration of S1-fermented soymilk extract. To further investigate the effect of aglycones in S1-fermented soymilk on DOCA-salt hypertensive rats, two dosages of EE in S1-fermented soymilk were tested on this animal model since EE contains approximately ten folds of aglycone forms of isoflavone than WE. The protective effects of EE from S1-fermented soymilk on differentiated PC-12 and SH-SY5Y cells were better than non-fermented soymilk. Moreover, both dosages of ethanol extract of S1-fermented soymilk administration exhibited hypotensive effects, especially the high dosage (0.8g/kg bw), in DOCA-salt hypertensive rate. The levels of angiotensin II and NO were improved by S1-fermented soymilk in the hypertensive rats. Two cytokines, TNF-α and IL-6, were reduced by S1-fermented soymilk administration in DOCA-salt hypertensive rats compared with rats administrated with non-fermented soymilk extract. The predominant functions of gut microbiota in the DOCA-salt hypertensive rats with different treatments will be investigated by metagenomic sequencing to reveal more in-depth mechanisms involved.