High-salt diet decreases mechanical thresholds in mice that is mediated by a CCR2-dependent mechanism

Causal relationship of salt intake with osteoarthritis: A Mendelian randomization analysis

Recent studies have demonstrated a correlation between salt intake (SI) and various diseases. However, it remains uncertain whether the relationship between SI (including salt added to food and sodium levels in urine) and benign osteoarthritis is causal. To investigate this, we conducted a 2-sample Mendelian randomization (MR) analysis to estimate the causal impact of SI on osteoarthritis (OA). A genome-wide association study of salt added to food and sodium in urine was used as the exposure, while hip osteoarthritis, knee osteoarthritis, and rheumatoid arthritis were defined as the outcomes. Inverse variance weighting (IVW) was used to calculate causal estimates, and sensitivity analyses were performed using methods including weighted mode, weighted median, MR-Egger, and Bayesian weighted MR. All statistical analyses were conducted using R software. Our results, primarily based on the IVW method, support the existence of a causal relationship between salt added to food and knee osteoarthritis (KOA). Specifically, salt added to food was associated with a decreased risk of KOA (OR = 1.248, P = .024, 95% CI: 1.030-1.512). This study is the first MR investigation exploring the causal relationship between salt added to food and KOA, potentially providing new insights and a theoretical basis for the prevention and treatment of KOA in the future.

Trained immunity induced by high-salt diet impedes stroke recovery

A high-salt diet (HSD) elicits sustained sterile inflammation and worsens tissue injury. However, how this occurs after stroke, a leading cause of morbidity and mortality, remains unknown. Here, we report that HSD impairs long-term brain recovery after intracerebral hemorrhage, a severe form of stroke, despite salt withdrawal prior to the injury. Mechanistically, HSD induces innate immune priming and training in hematopoietic stem and progenitor cells (HSPCs) by downregulation of NR4a family and mitochondrial oxidative phosphorylation. This training compromises alternative activation of monocyte-derived macrophages (MDMs) without altering the initial inflammatory responses of the stroke brain. Healthy mice transplanted with bone marrow from HSD-fed mice retain signatures of reduced MDM reparative functions, further confirming a persistent form of innate immune memory that originates in the bone marrow. Loss of NR4a1 in macrophages recapitulates HSD-induced negative impacts on stroke outcomes while gain of NR4a1 enables stroke recovery in HSD animals. Together, we provide the first evidence that links HSD-induced innate immune memory to the acquisition of persistent dysregulated inflammatory responses and unveils NR4a1 as a potential therapeutic target.

Activation of Granulocytes in Response to a High Protein Diet Leads to the Formation of Necrotic Lesions in the Liver

In their aspiration to become healthy, people are known to follow extreme diets. However, the acute impact on organs regulating systemic metabolism is not well characterized. Here, we investigated the acute impact of six extreme diets on the liver in mice. Most diets did not lead to clear pathology after short-term feeding. However, two weeks of feeding with a high protein diet (HPD) resulted in an acute increase of liver enzymes in the blood, indicative of liver damage. Histology revealed the formation of necrotic lesions in this organ which persisted for several weeks. Flow cytometric analysis of hepatic immune cell populations showed that HPD feeding induced activation of macrophages and neutrophils. Neutralization of the pro-inflammatory cytokine IL-1β or depletion of macrophages with clodronate-loaded liposomes or with genetic models did not ameliorate liver necrosis. In contrast, the depletion of neutrophils prevented HPD-induced hepatic inflammation. After prolonged feeding, HPD-feeding was associated with a strong increase of the cytokines IL-10 and IL-27, suggesting that anti-inflammatory mediators are activated to prevent nutrient-overload-induced damage to the liver. In summary, whereas our data indicates that most extreme diets do not have a major impact on the liver within two weeks, diets with a very high protein content may lead to severe, acute hepatic damage and should therefore be avoided.

The modulatory effect of high salt on immune cells and related diseases

BACKGROUND

The adverse effect of excessive salt intake has been recognized in decades. Researchers have mainly focused on the association between salt intake and hypertension. However, studies in recent years have proposed the existence of extra-renal sodium storage and provided insight into the immunomodulatory function of sodium.

OBJECTIVES

In this review, we discuss the modulatory effects of high salt on various innate and adaptive immune cells and immune-regulated diseases.

METHODS

We identified papers through electronic searches of PubMed database from inception to March 2022.

RESULTS

An increasing body of evidence has demonstrated that high salt can modulate the differentiation, activation and function of multiple immune cells. Furthermore, a high-salt diet can increase tissue sodium concentrations and influence the immune responses in microenvironments, thereby affecting the development of immune-regulated diseases, including hypertension, multiple sclerosis, cancer and infections. These findings provide a novel mechanism for the pathology of certain diseases and indicate that salt might serve as a target or potential therapeutic agent in different disease contexts.

CONCLUSION

High salt has a profound impact on the differentiation, activation and function of multiple immune cells. Additionally, an HSD can modulate the development of various immune-regulated diseases.

The Bidirectional Signal Communication of Microbiota-Gut-Brain Axis in Hypertension

Hypertension is a critical risk factor of cardiovascular diseases. A new concept of microbiota-gut-brain axis has been established recently, mediating the bidirectional communication between the gut and its microbiome and the brain. Alterations in bidirectional interactions are believed to be involved in the blood pressure regulation. Neuroinflammation and increased sympathetic outflow act as the descending innervation signals from the brain. Increased sympathetic activation plays a recognized role in the genesis of hypertension. The present evidence demonstrates that gut dysbiosis is associated with central nervous system neuroinflammation. However, how the gut influences the brain remains unclear. We reviewed the roles of neuroinflammation and gut microbiota and their interactions in the pathogenesis of hypertension and described the ascending signaling mechanisms behind the microbiota-gut-brain axis in detail. Additionally, the innovative prohypertensive mechanisms of dietary salt through the microbiota-gut-brain axis are summarized. The bidirectional communication mechanisms were proposed for the first time that the descending signals from the brain and the ascending connections from the gut form a vicious circle of hypertension progression, acting as a premise for hypertension therapy.

High Estimated 24-Hour Urinary Sodium Excretion Is Related to Symptomatic Knee Osteoarthritis: A Nationwide Cross-Sectional Population-Based Study

OBJECTIVES

High salt intake results in various harmful effects on human health including hypertension, cardiovascular disease, and reduced bone density. Despite this, there are very few studies in the literature that have investigated the association between sodium intake and osteoarthritis (OA). Therefore, we aimed to explore these associations in a Korean population.

METHODS

This study used cross-sectional data from adult subjects aged 50-75 years from two consecutive periods of the Korean National Health and Nutrition Examination Survey V-VII (2010-2011 and 2014-2016). The estimated 24-hour urinary sodium excretion (24HUNa) was used as a surrogate marker of salt intake. In the 2010-2011 dataset, knee OA (KOA) was defined as the presence of the radiographic features of OA and knee pain. The association between KOA and salt intake was analysed using univariable and multivariable logistic regression methods. For the sensitivity analysis, the same procedures were conducted on subjects with self-reported OA (SR-OA) with knee pain in the 2010-2011 dataset and any site SR-OA in the 2014-2016 dataset.

RESULTS

Subjects with KOA had significantly lower energy intake, but higher 24HUNa than those without KOA. The restricted cubic spline plots demonstrated a J-shaped distribution between 24HUNa and prevalent KOA. When 24HUNa was stratified into five groups (<2, 2-3, 3-4, 4-5 and ≥5 g/day), subjects with high sodium intake (≥5 g/day) had a higher risk of KOA (odds ratio [OR] = 1.64, 95% confidence interval [CI] 1.03-2.62) compared to the reference group (3-4 g/day) after adjusting for covariates. The sensitivity analysis based on SR-OA with knee pain showed that high sodium intake was also significantly associated with increased prevalence of OA (OR = 1.84, 95% CI 1.10-3.10) compared with the reference group. Regarding SR-OA at any site in the 2014-2016 dataset, estimated 24HUNa showed a significantly positive association with the presence of SR-OA after adjusting for potential confounders.

CONCLUSIONS

This nationwide Korean representative study showed a significant association between symptomatic KOA and high sodium intake (≥5 g/day). Avoidance of a diet high in salt might be beneficial as a non-pharmacologic therapy for OA.

Does Low Grade Systemic Inflammation Have a Role in Chronic Pain?

One of the major clinical manifestations of peripheral neuropathy, either resulting from trauma or diseases, is chronic pain. While it significantly impacts patients’ quality of life, the underlying mechanisms remain elusive, and treatment is not satisfactory. Systemic chronic inflammation (SCI) that we are referring to in this perspective is a state of low-grade, persistent, non-infective inflammation, being found in many physiological and pathological conditions. Distinct from acute inflammation, which is a protective process fighting against intruders, SCI might have harmful effects. It has been associated with many chronic non-communicable diseases. We hypothesize that SCI could be a predisposing and/or precipitating factor in the development of chronic pain, as well as associated comorbidities. We reviewed evidence from human clinical studies indicating the coexistence of SCI with various types of chronic pain. We also collated existing data about the sources of SCI and who could have it, showing that those individuals or patients having SCI usually have higher prevalence of chronic pain and psychological comorbidities. We thus elaborate on the need for further research in the connection between SCI and chronic pain. Several hypotheses have been proposed to explain these complex interactions.

Exposure to hypertonic solutions during pregnancy induces autism-like behaviors via the NFAT-5 pathway in offspring in a rat model

OBJECTIVES

to investigate the effects of hyperosmolar state (HS) on immune response and inflammation via the NFAT5 pathway and examine whether immune-mediated conditions trigger autism-like behavior in offspring.

METHODS

a pregnant rat model was performed by administering hyperosmotic solutions. Pregnant rats were divided into 2 main groups; control (group I) and hyperosmolar groups (group II). Control group rats were given % 0.25 NaCI (tap water) (n = 6), the Hyperosmolar (HO) group was further subdivided into 3 groups as; Group II a rats which were given % 3 hypertonic NaCl (n = 6), Group II b rats were given mineral water (% 3 NaHCO3+magnesium+calcium content) (n = 6), and Group II c rats were given Ayran (% 0.8 NaCl content) (n = 6). Their offspring were examined for behaviors, biochemical and histological abnormality.

RESULTS

in offspring, TNF- α, IL-17, NFAT-5, and NGF levels in the brain were significantly higher in hyperosmotic solution groups than in control rats. Exposure of pregnant rats to hyperosmotic solution resulted in autism-like behaviors in their offspring. Through immunohistochemical methods, we found that CA1 and CA2 of the hippocampus indicated decreased number of neurons in hyperosmotic solution groups compared with the control group.

CONCLUSIONS

our findings once again emphasized that the immune-mediated conditions involved in the pathophysiology of autism. NFAT5 pathway may be a key factor in the development of neuroinflammation by hyperosmotic solutions.

Sodium and its manifold impact on our immune system

The Western diet is rich in salt, and a high salt diet (HSD) is suspected to be a risk factor for cardiovascular diseases. It is now widely accepted that an experimental HSD can stimulate components of the immune system, potentially exacerbating certain autoimmune diseases, or alternatively, improving defenses against certain infections, such as cutaneous leishmaniasis. However, recent findings show that an experimental HSD may also aggravate other infections (e.g., pyelonephritis or systemic listeriosis). Here, we discuss the modulatory effects of a HSD on the microbiota, metabolic signaling, hormonal responses, local sodium concentrations, and their effects on various immune cell types in different tissues. We describe how these factors are integrated, resulting either in immune stimulation or suppression in various tissues and disease settings.