Possible predisposition of diabetic patients to hyperkalemia following administration of potassium-retaining diuretic, amiloride (MK 870)

Mitochondrial Uncoupling Coordinated With PDH Activation Safely Ameliorates Hyperglycemia via Promoting Glucose Oxidation

Uncoupling of mitochondrial respiration by chemical uncouplers has proven effective in ameliorating obesity, insulin resistance, and hyperglycemia. However, development of uncoupler-based therapy remains challenging due to its potentially lethal adverse effects. Here, we identify pyruvate dehydrogenase (PDH) as a key modifier of the toxicity profile of 2, 4-dinitrophenol (DNP), a prototypical mitochondrial uncoupler. PDH activation by dichloroacetic acid (DCA) protects mice from DNP-induced hyperlactacidemia, hyperthermia, and death while preserving the ability of DNP to promote fuel oxidation and improve insulin sensitivity in mice. Mechanistically, PDH activation switches on mitochondrial glucose oxidation to accommodate increased glycolytic flux, leading to reduced lactate secretion during uncoupler treatments. We devised a chemical screening strategy and discovered compound 6j as a dual-action compound that simultaneously activates PDH and uncouples mitochondrial respiration. Compound 6j exhibits an excellent efficacy and safety profile in restoring glucose homeostasis in diabetic mice. This work establishes a new principle to safely harness the power of chemical uncouplers for the treatment of metabolic disease.

6-Substituted Hexamethylene Amiloride (HMA) Derivatives as Potent and Selective Inhibitors of the Human Urokinase Plasminogen Activator for Use in Cancer

Metastasis is the cause of death in the majority (∼90%) of malignant cancers. The oral potassium-sparing diuretic amiloride and its 5-substituted derivative 5 -N, N-(hexamethylene)amiloride (HMA) reportedly show robust antitumor/metastasis effects in multiple in vitro and animal models. These effects are likely due, at least in part, to inhibition of the urokinase plasminogen activator (uPA), a key protease determinant of cell invasiveness and metastasis. This study reports the discovery of 6-substituted HMA analogs that show nanomolar potency against uPA, high selectivity over related trypsin-like serine proteases, and minimal inhibitory effects against epithelial sodium channels (ENaC), the diuretic and antikaliuretic target of amiloride. Reductions in lung metastases were demonstrated for two analogs in a late-stage experimental mouse metastasis model, and one analog completely inhibited formation of liver metastases in an orthotopic xenograft mouse model of pancreatic cancer. The results support further evaluation of 6-substituted HMA derivatives as uPA-targeting anticancer drugs.

Survival of extreme hyperkalemia

Severe hyperkalemia has been reported to lead to typical ECG changes, often reflecting cardiac abnormalities which finally lead to death in arrhythmias. The present report describes a 77-year-old male, who developed extreme hyperkalemia because of treatment with a potassium saving diuretic in combination with potassium supplementation and subsequent development of urinary retention. In spite of a maximal potassium value of 10.1 mmol/l only non-specific ECG-changes were found. The patient survived after an uneventful dialysis. Thus, extreme hyperkalemia may occur without typical ECG changes and serum potassium values exceeding 10 mmol/l may be survived.

Blood pressure drug therapy and electrolyte disturbances

Antihypertensive pharmacologic treatment may be associated with diverse disturbances of electrolyte homeostasis. These drug-induced disorders are relatively common, typically including hyponatraemia, hypokalaemia, hyperkalaemia, hypomagnesaemia, hypophosphataemia and hypercalcaemia. Diuretics, beta-blockers, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are particularly likely to cause these complications. Recognised risk factors include high-dosage regimens (especially diuretics), old age, diabetes and impairment of renal function. Strategies to prevent these adverse drug reactions involve careful consideration of risk factors and clinical and laboratory evaluation in the course of treatment.

Addison's disease and the regulation of potassium: the role of insulin and aldosterone

It is proposed that insulin has a cardinal role in the regulation of serum potassium levels in man, which may be of greater importance than the effect of insulin on glucose metabolism. Although the first described action of insulin was on glucose transport, it is a hormone with many functions some of which may operate in a metabolic hierarchy depending on the relative importance of the action required. Insulin also promotes the transport of potassium ions from the extracellular space to the intracellular space and it is suggested that there are occasions where this action may take place at the expense of glucose regulation. In metabolic terms, tight control of serum potassium is of greater importance than precise control of serum glucose, because quite small variations in serum potassium may cause death whereas wide variations in serum glucose may be tolerated. Serum potassium levels generally remain very stable despite large daily variations in potassium intake. It follows that potassium control mechanisms must be of outstanding efficiency as serious disturbances of potassium balance are relatively uncommon. 'Nature makes experiments on Man': shadowy but important physiological mechanisms that may almost be taken for granted in normal health are often brightly illuminated by unusual pathological conditions. This paper describes two remarkable patients who presented with extreme hyperkalaemia. This condition was the result of simultaneous insulin and aldosterone deficiency occurring because of concomitant diabetes and Addison's disease. Other medical conditions with disturbances in aldosterone, insulin and potassium control will be referred to in support of the hypothesis that insulin secretion is central to potassium regulation. This hypothesis explains the secondary disturbances in glucose metabolism that occurs in clinical situations where the primary problem is perturbation of potassium regulation.

GI262570, a Peroxisome Proliferator-Activated Receptor γ Agonist, Changes Electrolytes and Water Reabsorption from the Distal Nephron in Rats

Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists have been shown to have significant therapeutic benefits such as desirable glycemic control in type 2 diabetic patients; however, these agents may cause fluid retention in susceptible individuals. Since PPARgamma is expressed selectively in distal nephron epithelium, we studied the mechanism of PPARgamma agonist-induced fluid retention using male Sprague-Dawley rats treated with either vehicle or GI262570 (farglitazar), a potent PPARgamma agonist. GI262570 (20 mg/kg/day) induced a plasma volume expansion. The plasma volume expansion was accompanied by a small but significant decrease in plasma potassium concentration. Small but significant increases in plasma sodium and chloride concentrations were also observed. These changes in serum electrolytes suggested an activation of the renal mineralocorticoid response system; however, GI262570-treated rats had lower plasma levels of aldosterone compared with vehicle-treated controls. mRNA levels for a group of genes involved in distal nephron sodium and water absorption are changed in the kidney medulla with GI262570 treatment. In addition, due to a possible rebound effect on epithelial sodium channel (ENaC) activity, a low dose of amiloride did not prevent GI262570-induced fluid retention. On the contrary, the rebound effect after amiloride treatment potentiated GI262570-induced plasma volume expansion. This is at least partially due to a synergistic effect of GI262570 and the rebound from amiloride treatment on ENaCalpha expression. In summary, our current data suggest that GI262570 can increase water and sodium reabsorption in distal nephron by stimulating the ENaC and Na,K-ATPase system. This may be an important mechanism for PPARgamma agonist-induced fluid retention.

Drug-induced hyperkalemia: old culprits and new offenders

Prescribed medications, over-the-counter drugs, and nutritional supplements are used by many patients. Although most of these products are well tolerated, drug-induced hyperkalemia may develop in patients with underlying renal impairment or other abnormalities in potassium handling. Drug-induced hyperkalemia most often occurs from impaired renal potassium excretion. However, disturbed cellular uptake of a potassium load as well as excessive ingestion or infusion of potassium-containing substances may also occur. Physicians must be aware of medications that can precipitate hyperkalemia, how these drugs induce alterations in potassium homeostasis, and the patient characteristics that increase the risk of hyperkalemia.

Hyperkalemia in the elderly: drugs exacerbate impaired potassium homeostasis

OBJECTIVE

To review the pathophysiology underlying the predisposition to hyperkalemia in the elderly; the medications that disrupt potassium balance and promote the development of hyperkalemia in the elderly; the prevention of hyperkalemia in elderly patients treated with potassium-altering medications; and the appropriate management of hyperkalemia when it develops.

METHODS AND MAIN RESULTS

A MEDLINE search of the literature (1966-1996) using the terms hyperkalemia, drugs, elderly, and treatment was conducted and pertinent review articles, textbooks, and personal files were consulted. Elderly subjects appear to be predisposed to the development of hyperkalemia on the basis of both innate disturbances in potassium homeostasis and comorbid disease processes that impair potassium handling. Hyperkalemia in the elderly is most often precipitated by medications that impair cellular uptake or renal disposal of potassium. This electrolyte disorder is best prevented by recognition of at-risk physiology in the aged, avoidance of therapy with certain high-risk medications, and monitoring of plasma potassium concentration and renal function at intervals appropriate for the medication prescribed. Management of hyperkalemia entails identification of the clinical manifestations of severe hyperkalemia, stabilization of cardiac tissue, promotion of cellular potassium uptake, and ultimately removal of potassium from the body.

CONCLUSIONS

Geriatric patients should be considered at risk of developing hyperkalemia, especially when they are prescribed certain medications. Potassium levels should be monitored at appropriate intervals when these patients are treated with potassium-altering medications. Appropriate management of hyperkalemia in the elderly can avoid life-threatening neuromuscular and cardiac complications.

Diuretics and hyperkalaemia in diabetic ketoacidosis

Diabetic ketoacidosis (DKA) often presents with hyperkalaemia. We investigated whether it was more likely in patients taking potassium-retaining diuretics. A retrospective survey of all patients (552 cases) presenting in DKA between 1974 and 1984 was undertaken. Initial biochemical data were compared for patients recorded as taking potassium-retaining diuretics (7 cases) at the time of presentation with those taking potassium-losing diuretics (13 cases), and age matched control groups were selected from those who presented in DKA but were not taking diuretics. There was no significant difference in initial serum potassium levels between the diuretic treated groups. The serum sodium was higher in the control group than in the potassium losing group (p = 0.045) and the serum urea significantly lower (p = 0.045). We conclude that potassium-retaining diuretics do not predispose to hyperkalaemia in diabetic ketoacidosis.

Comparison of thiazides and amiloride in treatment of moderate hypertension

The biochemical disturbance produced by thiazide diuretics and by amiloride during treatment of moderate hypertension were compared. Two parallel studies were initiated. In one 40 patients with newly diagnosed hypertension were treated with metoprolol and a diuretic, either hydrochlorothiazide or amiloride. In a second study 38 patients receiving longstanding treatment with hypotensives and thiazides either continued the treatment or replaced the thiazide with amiloride. Initial biochemical assessments were compared with those after two years in the study. In previously untreated patients, thiazide produced a significant fall in plasma potassium and hyperuricaemia that did not occur with amiloride (p less than 0.001). Those patients receiving long term treatment for their hypertension who continued to take thiazides had persistent hypokalaemia and hyperuricaemia. Substitution with amiloride corrected the hypokalaemia and serum uric acid returned toward normal ranges, but this change was not statistically significant. Patients receiving long term treatment also had impaired glucose tolerance, this remained unchanged in those receiving thiazide but was corrected in those receiving amiloride. Compared with amiloride thiazides produced undesirable but reversible biochemical changes. As control of hypertension was equally effective with both preparations, we suggest that a combination of amiloride with a beta blocker in treatment of moderate hypertension in preferred.

Hyponatremia and hyperkalemia in relation to hyperglycemia in insulin-treated diabetic out-patients

Interrelations between glucose and electrolyte homeostasis were evaluated in 193 insulin-treated diabetic out-patients. All had normal serum creatinine and were studied during their everyday metabolic control. Although the patients were selected to be without proteinuria and ketonuria, they exhibited wide ranges of blood glucose values (2.5-29.5 mmol/l) and urine glucose excretions (0-301 mmol/mmol creatinine). Patients with blood glucose values within 2.5-10 mmol/l (n = 80) had entirely normal levels of serum sodium (140.6 +/- 2.7 (SD) versus 141.0 +/- 2.6 mmol/l) and potassium (4.35 +/- 0.38 versus 4.40 +/- 0.38 mmol/l) as compared with normals (n = 371). In contrast, diabetics with higher blood glucose concentrations (n = 113) showed hyponatremia (137.7 +/- 2.6 mmol/l, p less than 0.001) and a moderate increase of serum potassium (4.60 +/- 0.39 mmol/l, p less than 0.001). On stratification into classes of blood glucose, serum sodium declined from 142 to 135 mmol/l (r = -0.61, p less than 0.001), whereas serum potassium rose from 4.33 to 4.87 mmol/l (r = 0.37, p less than 0.001). Despite these reciprocal changes the urinary excretion rates relative to creatinine of sodium potassium and water rose with rising degrees of glycosuria (r = 0.24, p less than 0.001; r = 0.28, p less than 0.001; and r = 0.63, p less than 0.001, respectively). The decline in serum sodium represents a well-known osmoregulatory response to hyperglycemia. However, the rising level of serum potassium in virtual absence of renal failure and ketonuria suggests an abnormality in potassium homeostasis. Diabetic dysregulation, or rather insulin deficiency may be its cause.

Mechanism of action, pharmacokinetics, adverse effects, and therapeutic uses of amiloride hydrochloride, a new potassium-sparing diuretic

Amiloride hydrochloride is a new, orally administered, potassium-sparing diuretic with mild natriuretic and diuretic properties. Its primary site of action is the distal tubule of the nephron where it selectively blocks sodium transport, thereby inhibiting sodium-potassium exchange. The mechanism of action of amiloride is independent of aldosterone. It is excreted unmetabolized in the urine and feces. Peak serum levels are seen at three hours, and the serum half-life is six hours. The drug can probably be safely administered to patients with hepatic dysfunction but should be used cautiously, if at all, in patients with renal insufficiency. Amiloride is well tolerated, and serious toxicity is rare. It should prove useful in edematous states and hypertension. When amiloride is used in fixed combination with a thiazide diuretic the risk of hypokalemia is minimal.

Spironolactone and diabetic ketoacidosis

The authors describe a diabetic patient on spironolactone who, following a minor surgical procedure, developed ketoacidosis and life-threatening hyperkalaemia.

New drug evaluations amiloride (Midamor, Merck, Sharp and Dohme)

Amiloride is a potassium-sparing diuretic that is pharmacologically similar to triamterene. It has been widely used abroad for several years, alone and in combination with hydrochlorothiazide. As a potassium-sparing agent, amiloride appears to be approximately as effective as triamterene and spironolactone and to have a longer duration of action than triamterene, allowing once daily dosing. The diuretic effect of amiloride is mild, as are all agents that act at distal tubular sites. Amiloride appears to have an antihypertensive effect approximating that of the thiazides and spironolactone-an advantage over triamterene, which is devoid of antihypertensive effects. Amiloride will probably be most useful as a potassium-sparing agent in combination with the thiazide and loop diuretics. It should be kept in mind, however, that many patients on thiazide diuretics do not need supplemental potassium or potassium-sparing agents if they have no other complicating factors, such as digitalis therapy. When hypokalemia causes symptoms, a potassium-sparing agent have advantages over oral potassium supplements in patient tolerance and compliance. Because of the possibility of tumorigenicity and estrogenic side effects, spironolactone's popularity has been decreasing in recent years. Amiloride will probably be a strong competitor of triamterene and spironolactone because of its longer duration of action than triamterene and, from early indications (cf. ticrynafen), more benign side effects than spironolactone. The drug should be used with great caution, if at all, in patients with impaired renal function, however. The benefits of amiloride will have to be weighed against the cost of the drug in individual patients.

Paradoxical glucose-induced hyperkalemia. Combined aldosterone-insulin deficiency

Severe hyperkalemia associated with spontaneous hyperglycemia as well as with the intravenous infusions of glucose occurred in an insulin-requiring diabetic patient in the absence of potassium administration, the use of diuretics which inhibit urinary potassium excretion or acidemia. Metabolic balance studies revealed, in addition to diabets, the presence of isolated aldosterone deficiency of the hyporeninemic type. Intravenous glucose infusions (0.5 g/kg body weight) produced significant hyperkalemia but desoxycortisone acetate (DOCA) therapy (10 mg/day) prevented the glucose-induced hyperkalemia. In this patient, the serum potassium concentration increases after the intravenous infusions of glucose because there is insufficient aldosterone and insulin to reverse the transfer of potassium to the extracellular fluid which normally occurs after hypertonic infusions of glucose. Although DOCA replacement modifies the distribution of potassium in the extracellular fluid and blunts the hyperkalemic effect of intravenous infusions of glucose, a rise in the insulin level is required for the usual hypokalemic response to intravenously administered glucose. These studies illustrate the risk of raising blood glucose levels in patients with combined aldosterone and insulin deficiency and the tendency towards hyperkalemia in diabetic patients under certain clinical conditions.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.