A high-potassium diet reduces infarct size and improves vascular structure in hypertensive rats

Diet and Nutraceuticals for treatment and prevention of primary and secondary stroke: Emphasis on nutritional antiplatelet and antithrombotic agents

Ischemic stroke is a devastating disease that causes morbidity and mortality. Malnutrition following ischemic stroke is common in stroke patients. During the rehabilitation, the death rates of stroke patients are significantly increased due to malnutrition. Nutritional supplements such as protein, vitamins, fish, fish oils, moderate wine or alcohol consumption, nuts, minerals, herbal products, food colorants, marine products, fiber, probiotics and Mediterranean diets have improved neurological functions in stroke patients as well as their quality of life. Platelets and their mediators contribute to the development of clots leading to stroke. Ischemic stroke patients are treated with thrombolytics, antiplatelets, and antithrombotic agents. Several systematic reviews, meta-analyses, and clinical trials recommended that consumption of these nutrients and diets mitigated the vascular, peripheral, and central complications associated with ischemic stroke (Fig. 2). Particularly, these nutraceuticals mitigated the platelet adhesion, activation, and aggregation that intended to reduce the risks of primary and secondary stroke. Although these nutraceuticals mitigate platelet dysfunction, there is a greater risk of bleeding if consumed excessively. Moreover, malnutrition must be evaluated and adequate amounts of nutrients must be provided to stroke patients during intensive care units and rehabilitation periods. In this review, we have summarized the importance of diet and nutraceuticals in ameliorating neurological complications and platelet dysfunction with an emphasis on primary and secondary prevention of ischemic stroke.

Potassium status and the risk of type 2 diabetes, cardiovascular diseases, and mortality: a meta-analysis of prospective observational studies

Epidemiological evidence on the association between potassium and cardiometabolic outcomes remains controversial. This study aimed to examine associations of dietary intake and blood and urinary levels of potassium with risk of type 2 diabetes, cardiovascular disease (CVD), and mortality. Relevant prospective studies were retrieved through a comprehensive search of four electronic databases up to July 1, 2023. Random-effects models were used to pool the study-specific relative risks (RRs) and 95% confidence intervals (CIs). Fifty-six studies were included in this meta-analysis. A higher intake of potassium was significantly associated with a 16% lower risk of CVD (RR: 0.84, 95% CI: 0.78-0.90). Similar inverse associations were also observed between potassium intake and mortality. Each 1.0 g/d increment in potassium intake was associated with a decreased risk of CVD (RR: 0.85, 95% CI: 0.80-0.91) and all-cause mortality (RR: 0.93, 95% CI: 0.88-0.99). For blood and urinary potassium levels, higher level of blood potassium increased the risk of all-cause mortality by 23% (RR: 1.23, 95% CI: 1.11-1.36). The association of blood potassium levels with mortality was nonlinear (Pnon-linearit<0.001). However, urinary potassium levels were inversely associated with the risk of all-cause mortality (RR: 0.84, 95% CI: 0.76-0.93). Our findings support the benefits of moderate potassium consumption for primary prevention of chronic diseases and premature death.

Dietary potassium and the kidney: lifesaving physiology

Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.

Cerebrovascular events in hemodialysis patients; a retrospective observational study

BACKGROUND

This study reports findings in subjects who underwent brain imaging for any reason, and examined factors influencing cerebrovascular events (CVEs) in hemodialysis (HD) patients.

METHODS

We reviewed the files of patients on HD between January 2015 and January 2018. A total of 432 patients who underwent HD for at least 5 months by the January 2015 and who were older than 18 years were included in the study; 264 had been examined by cerebral computed tomography or magnetic resonance imaging examination within the 3 years. Cerebrovascular pathology was detected in 139 of 264 patients.

RESULTS

Of the 139 patients, 65 (24.62%) had ischemic lesions, 25 (9.47%) had hemorrhagic lesions, and 49 (18.56%) had cerebral small vessel disease (CSVD). We compared recorded data and later clinical findings between patients with and those without CVEs. The cause of end-stage renal disease was diabetes in 58.5% of patients with ischemic lesions, 52% in those with hemorrhagic lesions, and 55% in those with CSVD (P < 0.05). Patients with cerebrovascular ischemia were older (P = 0.0001) and had lower serum creatinine (sCr) (P = 0.0001) and higher serum C-reactive protein (CRP) (P = 0.002) levels than normal subjects. Hemorrhagic patients were older (P = 0.003) and had lower sCr (P = 0.003) and serum predialysis potassium (P = 0.003) and parathyroid hormone (PTH) (P = 0.004) levels than normal subjects. Patients with CSVD were older (P < 0.0001) and had lower sCr (P < 0.0001), phosphorus (P < 0.007), and PTH (P < 0.013) and higher CRP (P < 0.002) levels than normal subjects.

CONCLUSIONS

HD patients with CVEs are older and typically have diabetes mellitus and lower sCr levels.

Regulation of myogenic tone and structure of parenchymal arterioles by hypertension and the mineralocorticoid receptor

Proper perfusion is vital for maintenance of neuronal homeostasis and brain function. Changes in the function and structure of cerebral parenchymal arterioles (PAs) could impair blood flow regulation and increase the risk of cerebrovascular diseases, including dementia and stroke. Hypertension alters the structure and function of large cerebral arteries, but its effects on PAs remain unknown. We hypothesized that hypertension increases myogenic tone and induces inward remodeling in PAs; we further proposed that antihypertensive therapy or mineralocorticoid receptor (MR) blockade would reverse the effects of hypertension. PAs from 18-wk-old stroke-prone spontaneously hypertensive rats (SHRSP) were isolated and cannulated in a pressure myograph. At 50-mmHg intraluminal pressure, PAs from SHRSP showed higher myogenic tone (%tone: 39.1 ± 1.9 vs. 28.7 ± 2.5%, P < 0.01) and smaller resting luminal diameter (34.7 ± 1.9 vs. 46.2 ± 2.4 μm, P < 0.01) than those from normotensive Wistar-Kyoto rats, through a mechanism that seems to require Ca(2+) influx through L-type voltage-gated Ca(2+) channels. PAs from SHRSP showed inward remodeling (luminal diameter at 60 mmHg: 55.2 ± 1.4 vs. 75.7 ± 5.1 μm, P < 0.01) and a paradoxical increase in distensibility and compliance. Treatment of SHRSP for 6 wk with antihypertensive therapy reduced PAs' myogenic tone, increased their resting luminal diameter, and prevented inward remodeling. In contrast, treatment of SHRSP for 6 wk with an MR antagonist did not reduce blood pressure or myogenic tone, but prevented inward remodeling. Thus, while hypertensive remodeling of PAs may involve the MR, myogenic tone seems to be independent of MR activity.

The effects of hypertension on the cerebral circulation

Maintenance of brain function depends on a constant blood supply. Deficits in cerebral blood flow are linked to cognitive decline, and they have detrimental effects on the outcome of ischemia. Hypertension causes alterations in cerebral artery structure and function that can impair blood flow, particularly during an ischemic insult or during periods of low arterial pressure. This review will focus on the historical discoveries, novel developments, and knowledge gaps in 1) hypertensive cerebral artery remodeling, 2) vascular function with emphasis on myogenic reactivity and endothelium-dependent dilation, and 3) blood-brain barrier function. Hypertensive artery remodeling results in reduction in the lumen diameter and an increase in the wall-to-lumen ratio in most cerebral arteries; this is linked to reduced blood flow postischemia and increased ischemic damage. Many factors that are increased in hypertension stimulate remodeling; these include the renin-angiotensin-aldosterone system and reactive oxygen species levels. Endothelial function, vital for endothelium-mediated dilation and regulation of myogenic reactivity, is impaired in hypertension. This is a consequence of alterations in vasodilator mechanisms involving nitric oxide, epoxyeicosatrienoic acids, and ion channels, including calcium-activated potassium channels and transient receptor potential vanilloid channel 4. Hypertension causes blood-brain barrier breakdown by mechanisms involving inflammation, oxidative stress, and vasoactive circulating molecules. This exposes neurons to cytotoxic molecules, leading to neuronal loss, cognitive decline, and impaired recovery from ischemia. As the population ages and the incidence of hypertension, stroke, and dementia increases, it is imperative that we gain a better understanding of the control of cerebral artery function in health and disease.

Doxycycline, a matrix metalloprotease inhibitor, reduces vascular remodeling and damage after cerebral ischemia in stroke-prone spontaneously hypertensive rats

Matrix metalloproteases (MMPs) are a family of zinc peptidases involved in extracellular matrix turnover. There is evidence that increased MMP activity is involved in remodeling of resistance vessels in chronic hypertension. Thus we hypothesized that inhibition of MMP activity with doxycycline (DOX) would attenuate vascular remodeling. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with DOX (50 mg·kg(-1)·day(-1) in the drinking water) for 6 wk. Untreated SHRSP were controls. Blood pressure was measured by telemetry during the last week. Middle cerebral artery (MCA) and mesenteric resistance artery (MRA) passive structures were assessed by pressure myography. MMP-2 expression in aortas was measured by Western blot. All results are means ± SE. DOX caused a small increase in mean arterial pressure (SHRSP, 154 ± 1; SHRSP + DOX, 159 ± 3 mmHg; P < 0.001). Active MMP-2 expression was reduced in aorta from SHRSP + DOX (0.21 ± 0.06 vs. 0.49 ± 0.13 arbitrary units; P < 0.05). In the MCA, at 80 mmHg, DOX treatment increased the lumen (273.2 ± 4.7 vs. 238.3 ± 6.3 μm; P < 0.05) and the outer diameter (321 ± 5.3 vs. 290 ± 7.6 μm; P < 0.05) and reduced the wall-to-lumen ratio (0.09 ± 0.002 vs. 0.11 ± 0.003; P < 0.05). Damage after transient cerebral ischemia (transient MCA occlusion) was reduced in SHRSP + DOX (20.7 ± 4 vs. 45.5 ± 5% of hemisphere infarcted; P < 0.05). In the MRA, at 90 mmHg DOX, reduced wall thickness (29 ± 1 vs. 22 ± 1 μm; P < 0.001) and wall-to-lumen ratio (0.08 ± 0.004 vs. 0.11 ± 0.008; P < 0.05) without changing lumen diameter. These results suggest that MMPs are involved in hypertensive vascular remodeling in both the peripheral and cerebral vasculature and that DOX reduced brain damage after cerebral ischemia.

Tempol, a superoxide dismutase mimetic, prevents cerebral vessel remodeling in hypertensive rats

Increased reactive oxygen species (ROS) production is involved in the pathogenesis of hypertension and stroke. The effects of ROS on cerebral vessels from hypertensive rats have not been studied. We hypothesized that tempol, a superoxide dismutase mimetic, would prevent middle cerebral artery (MCA) remodeling in stroke-prone spontaneously hypertensive rats (SHRSP). Six-week-old male SHRSP were treated with tempol (1mM) for 6weeks. The MCA was then removed and mounted in a pressure myograph to study tone generation, vessel reactivity, and passive vessel structure. Data are shown as mean±SEM, tempol vs. control. Plasma thiobarbituric acid reactive substances (TBARS) were decreased by tempol treatment (14.15±1.46 vs. 20.55±1.25nM of malondialdehyde [MDA]/ml, p=0.008). Maximum serotonin-induced constriction was increased by tempol treatment, without changes in dilation to adenosine diphosphate or tone generation. At an intralumenal pressure of 80mmHg, tempol caused a dramatic increase in the MCA lumen diameter (246±5 vs. 207±3μm, p<0.001), outer diameter (281±5 vs. 241±3μm, p<0.001), lumen cross-sectional area, and vessel cross-sectional area. Collagen IV mRNA expressions were increased by 2.4-fold after tempol treatment. These results suggest that ROS are involved in the remodeling of the cerebral vasculature of SHRSP and that ROS scavenging can attenuate this process.

11beta-hydroxysteroid dehydrogenase type II inhibition causes cerebrovascular remodeling and increases infarct size after cerebral ischemia

Direct mineralocorticoid receptor (MR) activation with deoxycorticosterone acetate has deleterious effects on the cerebral vasculature. Inhibition of 11beta-hydroxysteroid dehydrogenase type II (11betaHSD2) mimics the detrimental effects of elevated mineralocorticoids in the heart, but the effect of enzyme inactivation on the cerebral vasculature is unknown. Therefore, we hypothesized that systemic 11betaHSD2 inhibition with carbenoxolone (CBX) would cause remodeling of the middle cerebral artery (MCA) and increase the damage caused by cerebral ischemia. Six-week-old male Sprague Dawley rats were divided into control and CBX (2.5 mg/d) + 0.9% NaCl treated. After 4 wk treatment, rats were used to assess either structure and reactivity of the MCA or the response to cerebral ischemia using the MCA occlusion technique. Cerebral damage was assessed by 2,3,5-triphenyltetrazolium chloride staining and expressed as a percentage of the hemisphere infarcted. CBX treatment increased systolic blood pressure (153.2 +/- 7.3 vs. 122.1 +/- 4.4 mm Hg; P < 0.05) compared with control rats. MCAs from CBX treated rats were smaller and stiffer than control MCAs over a range of intralumenal pressures, indicating inward remodeling of the vessel. CBX treatment significantly increased ischemic cerebral infarct size compared with control rats (27.1 +/- 5.4% vs. 14.8 +/- 4.2%; P < 0.05). These data indicate that inhibition of 11betaHSD2, and, thus, disproportionate glucocorticoid activation of the MR, results in remodeling of the MCA and worsens the outcome of cerebral ischemia, further underscoring the importance of understanding the mechanism by which MR activation leads to cerebrovascular disease.

Dietary potassium supplementation improves vascular structure and ameliorates the damage caused by cerebral ischemia in normotensive rats

Background

Dietary potassium supplementation in hypertensive rats is cardioprotective. This protection includes a blood pressure independent reduction in the amount of damage caused by cerebral ischemia. Therefore, we hypothesized that dietary potassium supplementation would improve the outcome of ischemic stroke by improving cerebral vessel structure in normotensive rats.

Methods

Wistar Kyoto (WKY) rats were fed a high (HK) or low potassium (LK) diet for six weeks from six weeks of age. At the end of treatment, cerebral ischemia was induced by middle cerebral artery (MCA) occlusion and the resultant infarct was quantified and expressed as a percentage of the hemisphere infarcted (%HI). MCA structure was assessed in an additional group of rats using a pressurized arteriograph.

Results

The cerebral infarct was significantly smaller in rats fed the HK diet, compared to rats fed the LK diet (21 ± 5.4 vs 33.5 ± 4.8 %HI HK vs LK p < 0.05). Vessel structure was improved in WKY rats fed the HK diet as indicated by an increase in the MCA lumen (298 ± 6.3 vs 276 ± 3.9 μm HK vs LK p < 0.05) and outer diameters (322 ± 7.6 vs 305 ± 4.8 μm HK vs LK p < 0.05). Wall thickness and area were unchanged, suggesting an outward euthrophic remodelling process. The HK diet had no effect on body weight or telemetry blood pressure.

Conclusion

These studies are the first to show a beneficial effect of dietary potassium in rats with normal blood pressure.

Is the mineralocorticoid receptor a potential target for stroke prevention?

In recent years, it has become increasingly clear that the extra-renal effects of aldosterone play an important role in the pathogenesis of cardiovascular disease. Stroke is one of the leading causes of death in the Western world, and MR (mineralocorticoid receptor) antagonism is a potential preventative therapy for patients at risk of both ischaemic and haemorrhagic strokes. This protective effect of MR antagonism appears to occur at the level of the cerebral vasculature and may be related to the expression and activation of the EGFR (epidermal growth factor receptor) and the degree of vessel wall collagen deposition.

Intact female stroke-prone hypertensive rats lack responsiveness to mineralocorticoid receptor antagonists

Data from the Framingham Heart Study suggest that women may be more sensitive to the deleterious cardiovascular remodeling effects of aldosterone. Previous studies from our laboratory have shown that chronic treatment with spironolactone, a mineralocorticoid receptor (MR) antagonist, decreases ischemic cerebral infarct size and prevents remodeling of the middle cerebral artery (MCA) in male spontaneously hypertensive stroke-prone rats (SHRSP). Therefore, we hypothesized that MR antagonism would reduce ischemic infarct size and prevent MCA remodeling in female SHRSP. Six-week-old female SHRSP were treated for 6 wk with spironolactone (25 or 50 mg.kg(-1).day(-1)) or eplerenone (100 mg.kg(-1).day(-1)) and compared with untreated controls. At 12 wk, cerebral ischemia was induced for 18 h using the intraluminal suture occlusion technique, or the MCA was isolated for analysis of passive structure using a pressurized arteriograph. MR antagonism had no effect on infarct size or passive MCA structure in female SHRSP. To study the potential effects of estrogen, the above experiments were repeated in bilaterally ovariectomized (OVX) female SHRSP treated with spironolactone (25 mg.kg(-1).day(-1)). Infarct size and vessel structure in OVX SHRSP were not different from control SHRSP. Spironolactone had no effect on infarct size in OVX SHRSP. However, MCA lumen and outer diameters were increased in spironolactone-treated OVX SHRSP, suggesting an effect of estrogen. Cerebral artery MR expression, assessed by Western blotting, was increased in female, compared with male, SHRSP. These studies highlight an apparent sexual dimorphism of MR expression and activity in the cerebral vasculature from hypertensive rats.

Spironolactone improves structure and increases tone in the cerebral vasculature of male spontaneously hypertensive stroke-prone rats

BACKGROUND

Previous studies show that ischemic cerebral infarct size is related to cerebral vessel structure. Spironolactone, a mineralocorticoid receptor antagonist, decreases ischemic cerebral infarct size in male spontaneously hypertensive stroke-prone rats (SHRSP). Therefore, we hypothesized that chronic spironolactone treatment would improve cerebral artery structure in the SHRSP.

METHODS

Six-week-old male SHRSP were treated with spironolactone (2.5 mg/day) for 6 weeks and were compared to untreated control SHRSP and normotensive Wistar Kyoto (WKY) rats. Using a pressurized arteriograph, structural measurements of the middle cerebral artery (MCA) were taken under passive (calcium-free), zero-flow conditions. Myogenic tone was calculated from active and passive measurements taken at 75 and 125 mmHg. Mean arterial pressure was measured using radiotelemetry.

RESULTS

Myogenic tone was increased only at 75 mmHg in the spironolactone-treated SHRSP compared to control rats. The MCA lumen and outer diameters were increased in the spironolactone-treated SHRSP compared to control SHRSP, but were not different from WKY rats, indicating a decrease in vascular remodeling. There was no effect of spironolactone on blood pressure, suggesting that this is a blood pressure-independent effect.

CONCLUSION

Increased myogenic tone and lumen diameter in the spironolactone-treated SHRSP may be responsible for the protective role of spironolactone in ischemic stroke.