Effects of heparin treatments in vivo and in vitro on adrenal angiotensin II receptors and angiotensin II-induced aldosterone production in rats

A comprehensive guide to the pharmacologic regulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 entry receptor

The recent emergence of coronavirus disease-2019 (COVID-19) as a global pandemic has prompted scientists to address an urgent need for defining mechanisms of disease pathology and treatment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, employs angiotensin converting enzyme 2 (ACE2) as its primary target for cell surface attachment and likely entry into the host cell. Thus, understanding factors that may regulate the expression and function of ACE2 in the healthy and diseased body is critical for clinical intervention. Over 66% of all adults in the United States are currently using a prescription drug and while earlier findings have focused on possible upregulation of ACE2 expression through the use of renin angiotensin system (RAS) inhibitors, mounting evidence suggests that various other widely administered drugs used in the treatment of hypertension, heart failure, diabetes mellitus, hyperlipidemias, coagulation disorders, and pulmonary disease may also present a varied risk for COVID-19. Specifically, we summarize mechanisms on how heparin, statins, steroids and phytochemicals, besides their established therapeutic effects, may also interfere with SARS-CoV-2 viral entry into cells. We also describe evidence on the effect of several vitamins, phytochemicals, and naturally occurring compounds on ACE2 expression and activity in various tissues and disease models. This comprehensive review aims to provide a timely compendium on the potential impact of commonly prescribed drugs and pharmacologically active compounds on COVID-19 pathology and risk through regulation of ACE2 and RAS signaling.

Heparin-induced hyperkalemia in an extremely-low-birth-weight infant: a case report

Heparin may cause hyperkalemia by blocking aldosterone biosynthesis in the adrenal gland. Dizygotic twin sisters were born by Cesarean section at 25 weeks' gestation. The younger sister developed acute hyperkalemia (7.4 mEq/L) at 10 days of age. At the time of the development of the hyperkalemia, there were no signs of systemic infection, cardiac or renal failure, adrenal insufficiency, or sudden anemia. She was receiving no medication other than heparin to maintain the vascular catheter. Heparin was changed to dalteparin at 12 days of age. The plasma potassium level normalized after 14 days of age. After this change, the urinary potassium concentration and the aldosterone and plasma renin activity increased. The urinary aldosterone levels before and after the changes were 31 and 183 pg/μg creatinine, respectively. When heparin-induced hyperkalemia is suspected, stopping the heparin administration facilitates diagnosis and treatment; if anticoagulant therapy is required; one treatment option is changing from unfractionated heparin to low-molecular-weight heparin.

Heparin-induced hyperkalemia confirmed by drug rechallenge

Subcutaneous heparin is commonly used as a prophylaxis against deep venous thrombosis in a wide variety of hospitalized patients. As with most medications, heparin has a significant side effect profile; heparin-induced hyperkalemia is an unusual but well described side effect. To increase awareness of heparin-induced hyperkalemia and of those patients at greatest risk, we present two cases of documented hyperkalemia induced by heparin and reconfirmed by drug rechallenge.

Heparin-induced hyperkalemia in chronic hemodialysis patients: comparison of low molecular weight and unfractionated heparin

Aldosterone suppression and subsequent hyperkalemia are well described reversible side effects of prolonged treatment with heparin. This study was designed to examine whether the discontinuous use of heparin three times a week to prevent thrombosis formation during hemodialysis sessions could also induce hypoaldosteronism and might contribute to increased predialysis kalemia in hemodialysis patients. Two different heparinization regimens were prospectively compared in a crossover study of 11 chronic hemodialysis patients. During 2 consecutive weeks, the patients were dialyzed each week with either their usual doses of unfractionated heparin (UH) (6,160 IU +/- 1,350 IU) or low molecular weight heparin (LMWH) (15 anti-Xa activity [aXa] U/kg + 5 aXa U/kg/h). In all but 2 patients, the predialysis level of plasma K+ was higher with UH than with LMWH, and the mean value was higher (5.66+/-0.83 versus 5.15+/-0.68 mM, p = 0.01) while no differences in the predialysis plasma concentrations of creatinine, phosphate, urea, and bicarbonate were observed, excluding the potential role of differences in diet and dialysis efficacy in explaining the higher plasma K+ concentration with UH. The mean plasma aldosterone to plasma renin activity (pRA) ratio was higher with LMWH than with UH (149.54+/-123.1 versus 111.91+/-86.22 pg/ng/ h, p < 0.05). Individual plasma aldosterone values were found to be correlated to pRAs both during the UH period and the LMWH period, and the slope of the positive linear relation between plasma aldosterone and pRA was lower during the UH treatment period (63 versus 105 pg/ng/h). Finally, a negative linear correlation was found between the differences in individual predialysis plasma K+ observed during the 2 protocols and the differences in the corresponding plasma aldosterone levels, suggesting a link between the higher kalemia and the lower aldosterone responsiveness to angiotensin with unfractionated heparin. Although it cannot be concluded whether or not LMWH inhibits aldosterone synthesis, should LMWH decrease aldosterone production, this side effect is 33% less marked than that of UH so that the predialysis plasma K+ levels are 10% lower. This property makes LMWH use preferable to that of UH in patients with elevated predialysis kalemia.

Vascular remodeling and mineralocorticoids

Circulating mineralocorticoid hormones are so named because of their important homeostatic properties that regulate salt and water balance via their action on epithelial cells. A broader range of functions in nonclassic target cellular sites has been proposed for these steroids and includes their contribution to wound healing following injury. A chronic, inappropriate (relative to intravascular volume and dietary sodium intake) elevation of these circulating hormones evokes a wound healing response in the absence of tissue injury--a wound healing response gone awry. The adverse remodeling of vascularized tissues seen in association with chronic mineralocorticoid excess is the focus of this review.

Heparin-induced aldosterone suppression and hyperkalemia

PURPOSE

To review the effects of heparin and heparinoid compounds on aldosterone physiology and associated induction of hyperkalemia.

MATERIALS AND METHODS

A comprehensive literature search (of human and animal data) was carried out by computer and by using reference citations from primary sources.

RESULTS

Heparin and its congeners are predictable, potent inhibitors of aldosterone production. This inhibitory effect is specific for the zona glomerulosa; other corticosteroids are not affected. Aldosterone suppression occurs within a few days of initiation of therapy, is reversible, and is independent of either anticoagulant effect or route of administration. Decreases in aldosterone levels may occur with heparin dosages as low as 5,000 U BID. The most important, but probably not the only mechanism of aldosterone inhibition appears to involve reduction in both the number and affinity of the angiotensin-II receptors in the zona glomerulosa. Prolonged use of heparin causes marked reduction in the width of the adrenal zona glomerulosa.

CONCLUSIONS

Aldosterone suppression results in natriuresis and less predictably in decreased excretion of potassium. Greater than normal serum potassium levels occur in about 7% of patients, but marked hyperkalemia generally requires the presence of additional factors perturbing potassium balance (in particular, renal insufficiency, diabetes mellitus, or the use of certain medications). Heparin-induced increases in serum potassium need to be better anticipated by clinicians. Serum potassium levels should be monitored periodically in patients being given heparin for 3 or more days, and in patients at relatively high risk for hyperkalemia, the monitoring interval should probably be no greater than 4 days.

Chronic mineralocorticoid excess and cardiovascular remodeling

Chronic mineralocorticoid (MC) excess, whether due to elevated plasma aldosterone (ALDO) or deoxycorticosterone (DOC), is associated with a perivascular fibrosis of systemic and coronary arterioles. This remodeling of resistance vessels contributes to the appearance of hypertension. Chronic MC excess is also accompanied by cardiac myocyte necrosis, secondary to myocardial potassium depletion, and a subsequent reparative fibrosis that appears in the normotensive, nonhypertrophied right and hypertensive, hypertrophied left ventricles. Fibrosis contributes to the appearance of ventricular arrhythmias and dysfunction. Herein, clinical and experimental evidence linking chronic, inappropriate (relative to dietary sodium) elevations in circulating ALDO and DOC with these reactive and reparative forms of fibrous tissue formation in the heart and other tissues is presented.

Antihypertensive action of heparin: role of the renin-angiotensin aldosterone system and prostaglandins

Chronic subcutaneous administration of heparin consistently lowers blood pressure in hypertensive rats. This antihypertensive effect is related at least in part to a concomitant decrease in hematocrit. Groups of spontaneously hypertensive (SHR) and normotensive Wistar (NWR) rats were treated with subcutaneous heparin (700 U/d) for 6 weeks. Weekly determinations of systolic blood pressure (tail-cuff) and hematocrit were done. Peripheral plasma renin activity, plasma aldosterone, plasma prostaglandins (PGs) (PGF2 alpha, PGI2), thromboxane A2, and urinary kallikrein were measured. Blood pressure responses of acute and chronic heparin treatment to vasoconstrictor substances, including angiotensin I, angiotensin II, and norepinephrine, were determined. As before, heparin produced a significant (P < .01) decrease in hematocrit in both SHRs and NWRs, but a parallel decrease in blood pressure was noted only in SHRs. A significant (P < .001) increase in plasma renin activity was found in heparin-treated SHRs and NWRs; however, a corresponding elevation of plasma aldosterone level was noted only in heparin-treated NWR. Plasma aldosterone level significantly (P < .01) decreased in heparin-treated SHRs. Plasma PGs and urinary kallikrein levels were not different among the groups. The blood pressure responses to vasoconstrictor substances were essentially similar among the heparin-treated and control groups. These findings suggest that PGs or kallikrein have a slight or no role in determining the antihypertensive effect of heparin. Conversely, the results suggest that a reduced aldosterone level contributes to the antihypertensive mechanism of heparin.

Role of aldosterone in congestive heart failure

Antialdosterone therapy in patients with secondary hyperaldosteronism due to myocardial failure must accomplish the following: (1) reduce or preferably normalize plasma aldosterone levels by blockade of excessive synthesis, (2) antagonize the renal and systemic effects of aldosterone at its receptor sites, and (3) minimize the presence of multiple stimuli to aldosterone secretion. Fulfillment of these goals likely requires the blockade of angiotensin II-induced aldosterone secretion (ie, angiotensin-converting enzyme inhibition) with an antagonist of aldosterone receptors (ie, spironolactone [Aldactone]). Despite the potential for hyperkalemia with this combined use of medications, particularly in patients with impaired renal function, such therapy is likely to attenuate the salt-acquisitive state that is characteristic of myocardial failure.

Aldosterone and antialdosterone therapy in congestive heart failure

The pathophysiologic cycle that links myocardial failure with the appearance of congestive heart failure is not fully understood. It is clear, however, that an activation of several neurohormonal systems and the interplay between kidneys, adrenal glands, and heart contribute to abnormal sodium and water homeostasis. Aldosterone, the body's most potent mineralocorticoid hormone, contributes to intravascular and extravascular volume expansion, and thus to the appearance of symptomatic failure. Antialdosterone therapy in patients with secondary hyperaldosteronism due to heart failure must achieve one or more of the following goals: reduce or, preferably, normalize plasma aldosterone levels by limiting synthesis; antagonize the renal and systemic effects of aldosterone at its receptor sites; and eliminate or minimize the multiple stimuli to aldosterone secretion.

Dose dependent suppression of mineralocorticoid metabolism by different heparin fractions

One neglected side effect of heparin therapy is the inhibition of adrenal aldosterone production leading to occasionally life-threatening hyperkalaemia. This is only reported with (therapeutic) high doses (greater than or equal to 20.000 IU). The complex interplay of mineralocorticoid metabolites was studied in 29 subjects with unfractionated (UFH) and low molecular weight heparin (LMWH). Both heparins altered mineralocorticoid metabolism in a dose dependent manner. Whereas no effect was observed with UFH 2 x 5000 IU sc/day or LMWH 2500 a FXa U sc/day, higher doses significantly suppressed aldosterone and 18-hydroxycorticosterone production in plasma and urine. Three out of seven patients receiving UFH 3 x 7500 IU sc/day developed hyperkalaemia. This study shows the threshold dosage of UFH leading to suppression of mineralocorticoid metabolism in man and provides information that LMWH as well as UFH can suppress mineralocorticoid production. With respect to therapeutic implications it is important that LMWH at 2500 a FXa U sc/d had no effect on mineralocorticoid metabolism in contrast to UFH at a dosage currently used for prevention of thromboembolism (3 x 5000 IU sc/d).

A low molecular weight heparin decreases plasma aldosterone in patients with primary hyperaldosteronism

Four patients with primary hyperaldosteronism were treated with nadroparin 4100 or 6150 antiXa IU daily for 4 days. Plasma and urine sodium and potassium, and plasma aldosterone and renin were monitored before, during and after the study. After four days of treatment, and for the following two days, plasma aldosterone was decreased (by a mean of 49% on Day 6), and urinary Na/K was increased (3.7-fold). The direction of the changes was reversed on Day 8. The study has confirmed the effect of low molecular weight heparin on aldosterone, and makes it unlikely that it is related to inhibition of angiotensin II stimulation in these patients, as renin could not be detected in their plasma.