Mycophenolate Mofetil Attenuates DOCA-Salt Hypertension: Effects on Vascular Tone

Primary Role of the Kidney in Pathogenesis of Hypertension

Previous transplantation studies and the concept of 'nephron underdosing' support the idea that the kidney plays a crucial role in the development of essential hypertension. This suggests that there are genetic factors in the kidney that can either elevate or decrease blood pressure. The kidney normally maintains arterial pressure within a narrow range by employing the mechanism of pressure-natriuresis. Hypertension is induced when the pressure-natriuresis mechanism fails due to both subtle and overt kidney abnormalities. The inheritance of hypertension is believed to be polygenic, and essential hypertension may result from a combination of genetic variants that code for renal tubular sodium transporters or proteins involved in regulatory pathways. The renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) are the major regulators of renal sodium reabsorption. Hyperactivity of either the RAAS or SNS leads to a rightward shift in the pressure-natriuresis curve. In other words, hypertension is induced when the activity of RAAS and SNS is not suppressed despite increased salt intake. Sodium overload, caused by increased intake and/or reduced renal excretion, not only leads to an expansion of plasma volume but also to an increase in systemic vascular resistance. Endothelial dysfunction is caused by an increased intracellular Na+ concentration, which inhibits endothelial nitric oxide (NO) synthase and reduces NO production. The stiffness of vascular smooth muscle cells is increased by the accumulation of intracellular Na+ and subsequent elevation of cytoplasmic Ca++ concentration. In contrast to the hemodynamic effects of osmotically active Na+, osmotically inactive Na+ stimulates immune cells and produces proinflammatory cytokines, which contribute to hypertension. When this occurs in the gut, the microbiota may become imbalanced, leading to intestinal inflammation and systemic hypertension. In conclusion, the primary cause of hypertension is sodium overload resulting from kidney dysregulation.

Renal and hypothalamic inflammation in renovascular hypertension: role of afferent renal nerves

Renal denervation (RDN) is a potential therapy for drug-resistant hypertension. However, whether its effects are mediated by ablation of efferent or afferent renal nerves is not clear. Previous studies have implicated that renal inflammation and the sympathetic nervous system are driven by the activation of afferent and efferent renal nerves. RDN attenuated the renal inflammation and sympathetic activity in some animal models of hypertension. In the 2 kidney,1 clip (2K1C) model of renovascular hypertension, RDN also decreased sympathetic activity; however, mechanisms underlying renal and central inflammation are still unclear. We tested the hypothesis that the mechanisms by which total RDN (TRDN; efferent + afferent) and afferent-specific RDN (ARDN) reduce arterial pressure in 2K1C rats are the same. Male Sprague-Dawley rats were instrumented with telemeters to measure mean arterial pressure (MAP), and after 7 days, a clip was placed on the left renal artery. Rats underwent TRDN, ARDN, or sham surgery of the clipped kidney and MAP was measured for 6 wk. Weekly measurements of water intake (WI), urine output (UO), and urinary copeptin were conducted, and urine was analyzed for cytokines/chemokines. Neurogenic pressor activity (NPA) was assessed at the end of the protocol calculated by the depressor response after intraperitoneal injection of hexamethonium. Rats were euthanized and the hypothalamus and kidneys removed for measurement of cytokine content. MAP, NPA, WI, and urinary copeptin were significantly increased in 2K1C-sham rats, and these responses were abolished by both TRDN and ARDN. 2K1C-sham rats presented with renal and hypothalamic inflammation and these responses were largely mitigated by TRDN and ARDN. We conclude that RDN attenuates 2K1C hypertension primarily by ablation of afferent renal nerves which disrupts bidirectional renal neural-immune pathways.NEW & NOTEWORTHY Hypertension resulting from reduced perfusion of the kidney is dependent on renal sensory nerves, which are linked to inflammation in the kidney and hypothalamus. Afferent renal nerves are required for chronic increases in both water intake and vasopressin release observed following renal artery stenosis. Findings from this study suggest an important role of renal sensory nerves that has previously been underestimated in the pathogenesis of 2K1C hypertension.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

Immunosuppression by Mycophenolate Mofetil Mitigates Intrarenal Angiotensinogen Augmentation in Angiotensin II-Dependent Hypertension

Augmentation of intrarenal angiotensinogen (AGT) leads to further formation of intrarenal angiotensin II (Ang II) and the development of hypertensive kidney injury. Recent studies demonstrated that macrophages and the enhanced production of pro-inflammatory cytokines can be crucial mediators of renal AGT augmentation in hypertension. Accordingly, this study investigated the effects of immunosuppression by mycophenolate mofetil (MMF) on intrarenal AGT augmentation. Ang II (80 ng/min) was infused with or without daily administration of MMF (50 mg/kg) to Sprague-Dawley rats for 2 weeks. Mean arterial pressure (MAP) in Ang II infused rats was slightly higher (169.7 ± 6.1 mmHg) than the Ang II + MMF group (154.7 ± 2.0 mmHg), but was not statistically different from the Ang II + MMF group. MMF treatment suppressed Ang II-induced renal macrophages and IL-6 elevation. Augmentation of urinary AGT by Ang II infusion was attenuated by MMF treatment (control: 89.3 ± 25.2, Ang II: 1194 ± 305.1, and Ang II + MMF: 389 ± 192.0 ng/day). The augmentation of urinary AGT by Ang II infusion was observed before the onset of proteinuria. Elevated intrarenal AGT mRNA and protein levels in Ang II infused rats were also normalized by the MMF treatment (AGT mRNA, Ang II: 2.5 ± 0.2 and Ang II + MMF: 1.5 ± 0.1, ratio to control). Ang II-induced proteinuria, mesangial expansion and renal tubulointerstitial fibrosis were attenuated by MMF. Furthermore, MMF treatment attenuated the augmentation of intrarenal NLRP3 mRNA, a component of inflammasome. These results indicate that stimulated cytokine production in macrophages contributes to intrarenal AGT augmentation in Ang II-dependent hypertension, which leads to the development of kidney injury.

The IFNγ-PDL1 Pathway Enhances CD8T-DCT Interaction to Promote Hypertension

BACKGROUND

Renal T cells contribute importantly to hypertension, but the underlying mechanism is incompletely understood. We reported that CD8Ts directly stimulate distal convoluted tubule cells (DCTs) to increase sodium chloride co-transporter expression and salt reabsorption. However, the mechanistic basis of this pathogenic pathway that promotes hypertension remains to be elucidated.

METHODS

We used mouse models of DOCA+salt (DOCA) treatment and adoptive transfer of CD8⁺ T cells (CD8T) from hypertensive animals to normotensive animals in in-vivo studies. Co-culture of mouse DCTs and CD8Ts was used as in-vitro model to test the effect of CD8T activation in promoting sodium chloride co-transporter-mediated sodium retention and to identify critical molecular players contributing to the CD8T-DCT interaction. IFNγ (interferon γ)-KO mice and mice receiving renal tubule-specific knockdown of PDL1 were used to verify in-vitro findings. Blood pressure was continuously monitored via radio-biotelemetry, and kidney samples were saved at experimental end points for analysis.

RESULTS

We identified critical molecular players and demonstrated their roles in augmenting the CD8T-DCT interaction leading to salt-sensitive hypertension. We found that activated CD8Ts exhibit enhanced interaction with DCTs via IFN-γ-induced upregulation of MHC-I and PDL1 in DCTs, thereby stimulating higher expression of sodium chloride co-transporter in DCTs to cause excessive salt retention and progressive elevation of blood pressure. Eliminating IFN-γ or renal tubule-specific knockdown of PDL1 prevented T cell homing into the kidney, thereby attenuating hypertension in 2 different mouse models.

CONCLUSIONS

Our results identified the role of activated CD8Ts in contributing to increased sodium retention in DCTS through the IFN-γ-PDL1 pathway. These findings provide a new mechanism for T cell involvement in the pathogenesis of hypertension and reveal novel therapeutic targets.

Renal Inflammation Induces Salt Sensitivity in Male db/db Mice through Dysregulation of ENaC

BACKGROUND

Hypertension is considered a major risk factor for the progression of diabetic kidney disease. Type 2 diabetes is associated with increased renal sodium reabsorption and salt-sensitive hypertension. Clinical studies show that men have higher risk than premenopausal women for the development of diabetic kidney disease. However, the renal mechanisms that predispose to salt sensitivity during diabetes and whether sexual dimorphism is associated with these mechanisms remains unknown.

METHODS

Female and male db/db mice exposed to a high-salt diet were used to analyze the progression of diabetic kidney disease and the development of hypertension.

RESULTS

Male, 34-week-old, db/db mice display hypertension when exposed to a 4-week high-salt treatment, whereas equivalently treated female db/db mice remain normotensive. Salt-sensitive hypertension in male mice was associated with no suppression of the epithelial sodium channel (ENaC) in response to a high-salt diet, despite downregulation of several components of the intrarenal renin-angiotensin system. Male db/db mice show higher levels of proinflammatory cytokines and more immune-cell infiltration in the kidney than do female db/db mice. Blocking inflammation, with either mycophenolate mofetil or by reducing IL-6 levels with a neutralizing anti-IL-6 antibody, prevented the development of salt sensitivity in male db/db mice.

CONCLUSIONS

The inflammatory response observed in male, but not in female, db/db mice induces salt-sensitive hypertension by impairing ENaC downregulation in response to high salt. These data provide a mechanistic explanation for the sexual dimorphism associated with the development of diabetic kidney disease and salt sensitivity.

Mycophenolate mediated remodeling of gut microbiota and improvement of gut-brain axis in spontaneously hypertensive rats

Microbiota has a role in the host blood pressure (BP) regulation. The immunosuppressive drug mofetil mycophenolate (MMF) ameliorates hypertension. The present study analyzes whether MMF improves dysbiosis in a genetic model of hypertension. Twenty weeks old male spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were randomly divided into three groups: untreated WKY, untreated SHR, and SHR treated with MMF for 5 weeks. MMF treatment restored gut bacteria from the phyla Firmicutes and Bacteroidetes, and acetate- and lactate-producing bacteria to levels similar to those found in WKY, increasing butyrate-producing bacteria. MMF increased the percentage of anaerobic bacteria in the gut. The improvement of gut dysbiosis was associated with an enhanced colonic integrity and a decreased sympathetic drive in the gut. MMF inhibited neuroinflammation in the paraventricular nuclei in the hypothalamus. MMF increased the lower regulatory T cells proportion in mesenteric lymph nodes and Th17 and Th1 infiltration in aorta, improved aortic endothelial function and reduced systolic BP. This study demonstrates for the first time that MMF reduces gut dysbiosis in SHR. This effect could be related to its capability to improve gut integrity due to reduced sympathetic drive in the gut associated to the reduced brain neuroinflammation.

Mycophenolate Improves Brain-Gut Axis Inducing Remodeling of Gut Microbiota in DOCA-Salt Hypertensive Rats

Microbiota is involved in the host blood pressure (BP) regulation. The immunosuppressive drug mofetil mycophenolate (MMF) ameliorates hypertension. The present study analyzed whether MMF improves dysbiosis in mineralocorticoid-induced hypertension. Male Wistar rats were assigned to three groups: untreated (CTR), deoxycorticosterone acetate (DOCA)-salt, and DOCA treated with MMF for 4 weeks. MMF treatment reduced systolic BP, improved endothelial dysfunction, and reduced oxidative stress and inflammation in aorta. A clear separation in the gut bacterial community between CTR and DOCA groups was found, whereas the cluster belonging to DOCA-MMF group was found to be intermixed. No changes were found at the phylum level among all experimental groups. MMF restored the elevation in lactate-producing bacteria found in DOCA-salt joined to an increase in the acetate-producing bacteria. MMF restored the percentage of anaerobic bacteria in the DOCA-salt group to values similar to control rats. The improvement of gut dysbiosis was associated with an enhanced colonic integrity and a decreased sympathetic drive in the gut. MMF inhibited neuroinflammation in the paraventricular nuclei in the hypothalamus. This study demonstrates for the first time that MMF reduces gut dysbiosis in DOCA-salt hypertension models. This effect seems to be related to its capacity to improve gut integrity due to reduced sympathetic drive in the gut associated with reduced brain neuroinflammation.

Greater T Regulatory Cells in Females Attenuate DOCA-Salt-Induced Increases in Blood Pressure Versus Males

Hypertension is the most common risk factor for cardiovascular disease, causing over 18 million deaths a year. Although the mechanisms controlling blood pressure (BP) in either sex remain largely unknown, T cells play a critical role in the development of hypertension. Further evidence supports a role for the immune system in contributing to sex differences in hypertension. The goal of the current study was to first, determine the impact of sex on the renal T-cell profiles in DOCA-salt hypertensive males and females and second, test the hypothesis that greater numbers of T regulatory cells (Tregs) in females protect against DOCA-salt-induced increases in BP and kidney injury. Male rats displayed greater increases in BP than females following 3 weeks of DOCA-salt treatment, although increases in renal injury were comparable between the sexes. DOCA-salt treatment resulted in an increase in proinflammatory T cells in both sexes; however, females had more anti-inflammatory Tregs than males. Additional male and female DOCA-salt rats were treated with anti-CD25 to decrease Tregs. Decreasing Tregs significantly increased BP only in females, thereby abolishing the sex difference in the BP response to DOCA-salt. This data supports the hypothesis that Tregs protect against the development of hypertension and are particularly important for the control of BP in females.

Mycophenolate mofetil attenuates concanavalin A-induced acute liver injury through modulation of TLR4/NF-κB and Nrf2/HO-1 pathways

BACKGROUND

Acute liver injury (ALI) is a serious health condition associated with rising morbidity and sudden progression. This study was designed to investigate the possible hepatocurative potential of two dose levels (30 and 60 mg/kg) of Mycophenolate mofetil (MMF), an immune-suppressant agent, against Concanavalin A (Con A)-induced ALI in mice.

METHOD

A single dose of Con A (20 mg/kg, IV) was used to induce ALI in mice. MMF (30 mg/kg and 60 mg/kg) was administered orally for 4 days post Con A injection.

RESULTS

MMF (30 mg/kg) failed to cause significant amelioration in Con A-induced ALI while MMF (60 mg/kg) significantly alleviated Con A-induced ALI. Administration of MMF (60 mg/kg) significantly decreased Con A-induced increase in serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Additionally, MMF significantly restored the disrupted oxidant/antioxidants status induced by Con A. MMF caused marked increase in hepatic nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels. Moreover, MMF significantly reduced Con A-induced increase in the expression of hepatic toll-like receptor 4 (TLR4), nuclear factor kappa-B (NF-κB), tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ) and interleukin-1β (Il-1β). Also, MMF administration significantly decreased Con A-induced increase in the immune-expression of pro-apoptotic Bcl-2-associated X protein (Bax) and markedly increased Con A-induced decrease in the anti-apoptotic B-cell lymphoma 2 protein (Bcl2).

CONCLUSION

The observed ameliorative effect of MMF against Con A-induce ALI may be contributed to its anti-inflammatory, anti-oxidant and anti-apoptotic potentials taking into consideration that TLR4/NF-κB and Nrf2/HO-1 are the main implicated pathways. Schematic diagram summarizing the possible mechanisms underlying the ameliorative potential of Mycophenolate Mofetil against Con A-induced acute liver injury. Bax Bcl-2-associated X protein, Bcl2 B-cell lymphoma 2, MMF Mycophenolate mofetil, Con A Concanavalin A, GSH reduced glutathione, HO-1 Heme oxygenase-1, IL-1β Interleukin-1β, IFN-γ Interferon-γ, MDA Malondialdehyde, NF-κB Nuclear Factor Kappa B, Nrf2 Nuclear factor erythroid 2-related factor 2, NO Nitric Oxide, SOD Superoxide Dismutase, TLR4 Toll-like receptor 4, TNF-α tumor necrosis factor-α.

Arterial Hypertension and Interleukins: Potential Therapeutic Target or Future Diagnostic Marker?

Hypertension as a multifactorial pathology is one of the most important cardiovascular risk factors, affecting up to 30-40% of the general population. Complex immune responses are involved in the inflammatory mechanism of hypertension, with evidence pointing to increased inflammatory mediators even in prehypertensive patients. Increased vascular permeability, thrombogenesis, and fibrosis, effects that are associated with sustained hypertension, could be attributed to chronic inflammation. Chronic inflammation triggers endothelial dysfunction via increased production of ROS through proinflammatory cytokines. Increased serum level of proinflammatory cytokines such as IL-1β, IL-6, IL-8, IL-17, IL-23, TGFβ, and TNFα in hypertensive patients has been associated with either increased blood pressure values and/or end-organ damage. Moreover, some cytokines (i.e., IL-6) seem to determine a hypertensive response to angiotensin II, regardless of blood pressure values. Understanding hypertension as an inflammatory-based pathology gives way to new therapeutic targets. As such, conventional cardiovascular drugs (statins, calcium channels blockers, and ACEIs/ARBs) have shown additional anti-inflammatory effects that could be linked to their blood pressure lowering properties. Moreover, anti-inflammatory drugs (mycophenolate mofetil) have been shown to decrease blood pressure in hypertensive patients or prevent its development in normotensive individuals. Further research is needed to evaluate whether drugs targeting hypertensive-linked proinflammatory cytokines, such as monoclonal antibodies, could become a new therapeutic option in treating arterial hypertension.