The kidney is the most vascularised organ of the body. The blood vessels supply two different types of microcirculation in the cortex (glomerular) and in the medulla (peritubular), each exerting different functions. This microcirculation plays a major role in the oxygen supply to the kidney and ensures plasma filtration, electrolyte exchange and water reabsorption.¹

The endothelium is the single layer of cells that line all blood vessels, and forms the interface between the circulating blood and underlying tissue.² Anormal functioning of the endothelium can lead to reduced renal function and eventually kidney disease.³ Many mediators interact with the microcirculation of the kidney, including nitric oxide (NO). NO dilates the afferent and the efferent arterioles, increases the glomerular filtration rate and affects renal sodium handling in the tubules.¹

The bioavailability of NO may be reduced by rapid inactivation via excess reactive oxygen species (ROS).⁴ In addition, increased ROS can stimulate the production of pro-inflammatory and pro-fibrotic factors in the kidney which are often involved in development and progression of renal injury.³

Over time the kidney shows an age-associated reduction of function, such as a decline in glomerular filtration rate and renal blood flow, which is possibly driven by reduced renal bioavailability of NO. This can increase the susceptibility of the ageing kidney to injury.³ One in three Australians have an increased risk of kidney disease. There are many risk factors for developing kidney disease, including smoking, obesity and age (being 60 years or older), but there are two groups of people who have a higher risk: people with diabetes and those with high blood pressure.⁵

Supporting kidney health is an important preventative health goal, and ensuring good microcirculation facilitates this.

Ingredients to Support Microcirculation of the Kidney

Kidney Function

The use of therapeutics containing proanthocyanidins, particularly from Cocoa, is a convenient way to support kidney health. A cohort study of 948 elderly women conducted in Australia over five years found that increased consumption of dietary proanthocyanidins was associated with better renal function and substantially reduced renal disease-associated events. The mean total proanthocyanidin intake was 215 mg/day. Over 50% of total proanthocyanidin intake came from fruit (89 mg/day), chocolate (43 mg/day) and alcoholic beverages (32 mg/day). Those who consumed at least 141 mg/day of proanthocyanidins, had lower cystatin C serum levels (which provides an early indication of renal dysfunction), compared to those with lower intakes. Participants consuming the highest amount of proanthocyanidins (at least 229 mg/day) were at 65% lower risk of experiencing a five-year renal event, compared to those with the lowest intake (less than 141 mg/day).⁶

Resveratrol improves microcirculation and also protects the kidney. For example, pretreatment with a modest oral dose of Resveratrol protected against kidney injury caused by ischaemia/reperfusion in rats. There was a marked reduction in kidney dysfunction and tissue changes and the kidney antioxidant enzyme levels were restored. These effects were due to Resveratrol increasing the release of NO.⁷ The dose (5 mg/kg) corresponds to about 57 mg/day in a 70-kg human.

General Microcirculation

Other natural substances that improve microcirculation may also be of benefit. For example, Green Tea has been shown to significantly increase skin microcirculation, in an uncontrolled study involving 15 young and 15 older volunteers. Two cups of Green Tea were consumed daily, each made using a teabag containing 2.5 g of leaf, for 14 days.⁸ In vitro testing found EGCG, a major catechin in Green Tea, induced vasodilation in endothelial cells by rapid activation of eNOS, the endothelial isoform of nitric oxide synthase.⁹ In another study, Grape Seed Extract (150 mg/day extract, providing 136.5 mg/day of OPCs) administered to borderline hypertensive patients, significantly improved microcirculation measured in the foot, after 8 weeks.¹⁰

Support the Production of Nitric Oxide

A study with healthy volunteers found that a small amount of dark chocolate (6.3 g, containing 3.1 g of Cocoa solids and 30 mg of polyphenols) added to the diet for 18 weeks improved the formation of vasodilative NO, as measured by the increase in S-nitrosoglutathione in the plasma.¹¹

Curcumin, one of the major constituents of Turmeric can also upregulate eNOS in blood vessels, thereby increasing the bioavailability of NO. This has been verified in animal models with high oral doses. The scavenging of the superoxide anion by Curcumin contributed to the activity.^12,13 In vitro testing also found that Grape Seed Extract high in oligomeric procyanidins had a vasodilatory effect on endothelial cells by activating eNOS.¹⁴

Extensive research using mostly in vitro tests has revealed that Resveratrol stimulates NO production by a number of mechanisms, and, by reducing oxidative stress, Resveratrol prevents oxidative NO inactivation thereby enhancing NO bioavailability.¹⁵

Summary

The microcirculation, endothelium and bioavailability of nitric oxide are important for the health of the kidney. They can be supported by dietary intake of polyphenols and other natural compounds including Resveratrol, high quality Cocoa, Green Tea, Grape Seed Extract and Turmeric.

References

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13. Kukongviriyapan U, Pannangpetch P, Kukongviriyapan V, Donpunha W, Sompamit K, Surawattanawan P. Curcumin protects against cadmium-induced vascular dysfunction, hypertension and tissue cadmium accumulation in mice. Nutrients. 2014 Mar 21;6(3):1194-208.
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