Gut-Immune-Kidney Axis: Influence of Dietary Protein in Salt-Sensitive Hypertension

Associations of serum glucocorticoid levels on hypertension and blood pressure-related indicators: a nested case-control study in rural China

BACKGROUND

The relationship between glucocorticoids and hypertension has shown inconsistent findings in previous studies. To address this, our study employed a nested case-control design in rural areas to further investigate the association between serum glucocorticoid levels and hypertension, and blood pressure-related indicators.

METHODS

This study employed a nested case-control design, involving 560 pairs of hypertensive cases and matched controls. The concentrations of serum cortisol (F), cortisone (E) and 11-deoxycortisol (S) were determined using liquid chromatography-tandem mass spectrometry. We employed various methods, including generalized linear model (GLM), conditional logistic regression model, restricted cubic spline regression, subgroup analysis, interaction, and joint effects, with adjustments for multiple covariates to analyze the relationships between glucocorticoids, hypertension, and blood pressure-related indicators.

RESULTS

After multivariable adjustments, ln-F, ln-F/E, and ln-S were positively associated with SBP, DBP, pulse pressure (PP), and mean arterial pressure (MAP), while ln-E was negatively associated with DBP and MAP ( P  < 0.05). Interestingly, ln-S showed no statistically significant association with hypertension prevalence ( P  > 0.05), whereas ln-F and ln-F/E were positively associated with it ( P  < 0.05). The adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were 1.153 (1.011-1.315) for ln-F and 2.072 (1.622-2.645) for ln-F/E, respectively. In contrast, ln-E exhibited a negative association with hypertension prevalence (adjusted OR = 0.837, 95% CI 0.714-0.982). Moreover, a significant association was observed between the combined use of high-dose F/E and high-dose S with hypertension prevalence (adjusted OR = 3.273, 95% CI 2.013-5.321). Blood pressure indicators and hypertension prevalence significantly increased with elevated serum F and F/E concentrations ( P  < 0.05). Interaction analysis further revealed that among women, the positive association between F/E and hypertension prevalence was more pronounced than in men ( P  < 0.05), and S exhibited a more significant positive association with hypertension prevalence in the overweight population ( P  < 0.05).

CONCLUSION

Serum F/E and S levels demonstrated positive associations with hypertension and blood pressure-related indicators, and their combined influence exhibited a synergistic effect on hypertension. Notably, F, F/E, and S were associated with heightened hypertension risk, warranting particular attention in women and overweight populations.

Salt-Sensitive Hypertension and the Kidney

Salt-sensitive hypertension (SS-HT) is characterized by blood pressure elevation in response to high dietary salt intake and is considered to increase the risk of cardiovascular and renal morbidity. Although the mechanisms responsible for SS-HT are complex, the kidneys are known to play a central role in the development of SS-HT and the salt sensitivity of blood pressure (SSBP). Moreover, several factors influence renal function and SSBP, including the renin-angiotensin-aldosterone system, sympathetic nervous system, obesity, and aging. A phenotypic characteristic of SSBP is aberrant activation of the renin-angiotensin system and sympathetic nervous system in response to excessive salt intake. SSBP is also accompanied by a blunted increase in renal blood flow after salt loading, resulting in sodium retention and SS-HT. Obesity is associated with inappropriate activation of the aldosterone mineralocorticoid receptor pathway and renal sympathetic nervous system in response to excessive salt, and mineralocorticoid receptor antagonists and renal denervation attenuate sodium retention and inhibit salt-induced blood pressure elevation in obese dogs and humans. SSBP increases with age, which has been attributed to impaired renal sodium handling and a decline in renal function, even in the absence of kidney disease. Aging-associated changes in renal hemodynamics are accompanied by significant alterations in renal hormone levels and renal sodium handling, resulting in SS-HT. In this review, we focus mainly on the contribution of renal function to the development of SS-HT.

Dendritic cell epithelial sodium channel induced inflammation and salt-sensitive hypertension

PURPOSE OF REVIEW

Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular disease. Epithelial sodium channel (ENaC) plays a critical role in renal electrolyte and volume regulation and has been implicated in the pathogenesis of SSBP. This review describes recent advances regarding the role of ENaC-dependent inflammation in the development of SSBP.

RECENT FINDINGS

We recently found that sodium enters dendritic cells via ENaC, a process regulated by serum/glucocorticoid-regulated kinase 1 and epoxyeicosatrienoic acid 14,15. Sodium entry activates NADPH oxidase, leading to the production of isolevuglandins (IsoLGs). IsoLGs adduct self-proteins to form neoantigens in dendritic cells that activate T cells and result in the release of cytokines promoting sodium retention, kidney damage, and endothelial dysfunction in SSBP. Additionally, we described a novel mechanistic pathway involving ENaC and IsoLG-dependent NLRP3 inflammasome activation. These findings hold promise for the development of novel diagnostic biomarkers and therapeutic options for SSBP.

SUMMARY

The exact mechanisms underlying SSBP remain elusive. Recent advances in understanding the extrarenal role of ENaC have opened a new perspective, and further research efforts should focus on understanding the link between ENaC, inflammation, and SSBP.

Salt Sensitivity: Causes, Consequences, and Recent Advances

Salt (sodium chloride) is an essential nutrient required to maintain physiological functions. However, for most people, daily salt intake far exceeds their physiological need and is habitually greater than recommended upper thresholds. Excess salt intake leads to elevation in blood pressure which drives cardiovascular morbidity and mortality. Indeed, excessive salt intake is estimated to be responsible for ≈5 million deaths per year globally. For approximately one-third of otherwise healthy individuals (and >50% of those with hypertension), the effect of salt intake on blood pressure elevation is exaggerated; such people are categorized as salt sensitive and salt sensitivity of blood pressure is considered an independent risk factor for cardiovascular disease and death. The prevalence of salt sensitivity is higher in women than in men and, in both, increases with age. This narrative review considers the foundational concepts of salt sensitivity and the underlying effector systems that cause salt sensitivity. We also consider recent updates in preclinical and clinical research that are revealing new modifying factors that determine the blood pressure response to high salt intake.

Bioactive Peptides from Ruditapes philippinarum Attenuate Hypertension and Cardiorenal Damage in Deoxycorticosterone Acetate-Salt Hypertensive Rats

Hypertension is a common disease that affects human health and can lead to damage to the heart, kidneys, and other important organs. In this study, we investigated the regulatory effects of bioactive peptides derived from Ruditapes philippinarum (RPP) on hypertension and organ protection in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We found that RPPs exhibited significant blood pressure-lowering properties. Furthermore, the results showed that RPPs positively influenced vascular remodeling and effectively maintained a balanced water-sodium equilibrium. Meanwhile, RPPs demonstrated anti-inflammatory potential by reducing the serum levels of inflammatory cytokines (TNF-α, IL-2, and IL-6). Moreover, we observed the strong antioxidant activity of RPPs, which played a critical role in reducing oxidative stress and alleviating hypertension-induced damage to the aorta, heart, and kidneys. Additionally, our study explored the regulatory effects of RPPs on the gut microbiota, suggesting a possible correlation between their antihypertensive effects and the modulation of gut microbiota. Our previous studies have demonstrated that RPPs can significantly reduce blood pressure in SHR rats. This suggests that RPPs can significantly improve both essential hypertension and DOAC-salt-induced secondary hypertension and can ameliorate cardiorenal damage caused by hypertension. These findings further support the possibility of RPPs as an active ingredient in functional anti-hypertensive foods.

Functional NADPH oxidase 2 in T cells amplifies salt-sensitive hypertension and associated renal damage

Infiltrating T cells in the kidney amplify salt-sensitive (SS) hypertension and renal damage, but the mechanisms are not known. Genetic deletion of T cells (SSCD247-/-) or of the p67phox subunit of NADPH oxidase 2 (NOX2; SSp67phox-/-) attenuates SS hypertension in the Dahl SS rat. We hypothesized that reactive oxygen species produced by NOX2 in T cells drive the SS phenotype and renal damage. T cells were reconstituted by adoptively transferring splenocytes (∼10 million) from the Dahl SS (SS→CD247) rat, the SSp67phox-/- rat (p67phox→CD247), or only PBS (PBS→CD247) into the SSCD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters and studied at 8 wk of age. There were no detectable differences in mean arterial pressure (MAP) or albuminuria between groups when rats were maintained on a low-salt (0.4% NaCl) diet. After 21 days of high-salt diet (4.0% NaCl), MAP and albuminuria were significantly greater in SS→CD247 rats compared with p67phox→CD247 and PBS→CD247 rats. Interestingly, there was no difference between p67phox→CD247 and PBS→CD247 rats in albuminuria or MAP after 21 days. The lack of CD3+ cells in PBS→CD247 rats and the presence of CD3+ cells in rats that received the T cell transfer demonstrated the effectiveness of the adoptive transfer. No differences in the number of CD3+, CD4+, or CD8+ cells were observed in the kidneys of SS→CD247 and p67phox→CD247 rats. These results indicate that reactive oxygen species produced by NOX2 in T cells participates in the amplification of SS hypertension and renal damage.NEW & NOTEWORTHY Our current work used the adoptive transfer of T cells that lack functional NADPH oxidase 2 into a genetically T cell-deficient Dahl salt-sensitive (SS) rat model. The results demonstrated that reactive oxygen species produced by NADPH oxidase 2 in T cells participate in the amplification of SS hypertension and associated renal damage and identifies a potential mechanism that exacerbates the salt-sensitive phenotype.

Dietary Protein, Chronic Salt-Sensitive Hypertension, and Kidney Damage

It has been estimated that over a fifth of deaths worldwide can be attributed to dietary risk factors. A particularly serious condition is salt-sensitive (SS) hypertension and renal damage, participants of which demonstrate increased morbidity and mortality. Notably, a large amount of evidence from humans and animals has demonstrated that other components of the diet can also modulate hypertension and associated end-organ damage. Evidence presented in this review provides support for the view that immunity and inflammation serve to amplify the development of SS hypertension and leads to malignant disease accompanied by tissue damage. Interestingly, SS hypertension is modulated by changes in dietary protein intake, which also influences immune mechanisms. Together, the evidence presented in this review from animal and human studies indicates that changes in dietary protein source have profound effects on the gut microbiota, microbiota-derived metabolites, gene expression, immune cell activation, the production of cytokines and other factors, and the development of SS hypertension and kidney damage.

Microbiota-associated mechanisms underlying sexual dimorphism in hypertension

Consistent research over the last 20 years has shown that there are clear sex differences in the pathogenesis of hypertension, the leading risk factor for the development of cardiovascular diseases. More recently, there is evidence in both humans and experimental animal models that causally implicates the gut microbiota in hypertension. It therefore follows that sex differences in the gut microbiota may mediate the extent of disease between sexes. This new field is rapidly changing and advancing, and the purpose of this review is to cover the most up-to-date evidence regarding the sexual dimorphism of the gut microbiota and its potential influence on the differential manifestation of hypertension in males versus females. Emphasis will be placed on the mechanisms thought to contribute to these sex differences in both the gut microbiota and hypertension, including sex steroid hormones, gut-derived metabolites, the immune system, and pregnancy.

Gut microbiota and its metabolites - molecular mechanisms and management strategies in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major microvascular complications of diabetes mellitus and is also one of the serious risk factors in cardiovascular events, end-stage renal disease, and mortality. DKD is associated with the diversified, compositional, and functional alterations of gut microbiota. The interaction between gut microbiota and host is mainly achieved through metabolites, which are small molecules produced by microbial metabolism from exogenous dietary substrates and endogenous host compounds. The gut microbiota plays a critical role in the pathogenesis of DKD by producing multitudinous metabolites. Nevertheless, detailed mechanisms of gut microbiota and its metabolites involved in the occurrence and development of DKD have not been completely elucidated. This review summarizes the specific classes of gut microbiota-derived metabolites, aims to explore the molecular mechanisms of gut microbiota in DKD pathophysiology and progression, recognizes biomarkers for the screening, diagnosis, and prognosis of DKD, as well as provides novel therapeutic strategies for DKD.

The role and mechanism of gut microbiota-derived short-chain fatty in the prevention and treatment of diabetic kidney disease

Diabetic kidney disease (DKD), an emerging global health issue, is one of the most severe microvascular complications derived from diabetes and a primary pathology contributing to end-stage renal disease. The currently available treatment provides only symptomatic relief and has failed to delay the progression of DKD into chronic kidney disease. Recently, multiple studies have proposed a strong link between intestinal dysbiosis and the occurrence of DKD. The gut microbiota-derived short-chain fatty acids (SCFAs) capable of regulating inflammation, oxidative stress, fibrosis, and energy metabolism have been considered versatile players in the prevention and treatment of DKD. However, the underlying molecular mechanism of the intervention of the gut microbiota-kidney axis in the development of DKD still remains to be explored. This review provides insight into the contributory role of gut microbiota-derived SCFAs in DKD.