Hypertensive hypokalemic disorders

Population Target-Mediated Pharmacokinetic/Pharmacodynamic Modeling to Evaluate SPI-62 Exposure and Hepatic 11β-Hydroxysteroid Dehydrogenase Type 1 (HSD-1) Inhibition in Healthy Adults

INTRODUCTION

SPI-62 is a small-molecule 11β-hydroxysteroid dehydrogenase type 1 (HSD-1) inhibitor exhibiting complicated nonlinear pharmacokinetics (PK) in human. Previously, we developed a target-mediated drug disposition (TMDD) model to characterize the substantial nonlinear PK of SPI-62.

OBJECTIVE

The aim of the current analysis was to perform population PK/PD analysis to further link SPI-62 exposure (i.e., PK) with its response (i.e., inhibition of hepatic HSD-1 activity) to gain a quantitative understanding of the SPI-62 dose-exposure-response relationship.

METHODS

PK and PD data from the first-in-human (FIH) clinical trials, including single ascending dose (SAD) and multiple ascending dose (MAD) studies, were used for model development. During the model development process, the final model selection was based on biological and physiological plausibility, goodness-of-fit plots, stability of parameter estimates, and objective function value. The nonlinear-mixed effect modeling (NONMEM) software was used for both the implementation of the PK/PD model and model simulation. SPI-62 plasma levels and hepatic HSD-1 inhibition over time following various dose regimens were simulated.

RESULTS

The final model was a two-compartment TMDD model component for SPI-62 and an inhibitory Imax model component for hepatic HSD-1 activity. The TMDD-hepatic PD model that we established adequately characterized all remarkable PK and PD behaviors of SPI-62, such as extremely low plasma exposures following the first low doses, nonlinear PK turned into linear PK after repeated low doses, and substantial and long-lasting hepatic HSD-1 inhibition following low doses. SPI-62 was estimated to bind to the target with a second-order association rate constant (Kon) of 8.43 nM-1 h-1 and first-order dissociation rate constant (Koff) value of 0.229 h-1, indicating that SPI-62 binds rapidly to, and dissociates slowly from, its pharmacological target. The estimated target capacity (Rtot) of 5460 nmol corresponds to approximately 2.2 mg of SPI-62, which comports well with the dose range in which PK nonlinearity is prominent. Model simulation results reveal that a 6 mg once-daily regimen can lead to long-lasting and substantial hepatic HSD-1 inhibition.

CONCLUSIONS

A population TMDD-PD model that explains SPI-62 nonlinear PK and hepatic HSD-1 inhibition following different dose regimens in healthy adults was successfully established. Our simulation results provide a solid foundation for model-informed development of SPI-62.

Role of Environmental Toxicants in the Development of Hypertensive and Cardiovascular Diseases

The incidence of hypertension with diabetes mellitus (DM) as a co-morbid condition is on the rise worldwide. In 2000, an estimated 972 million adults had hypertension, which is predicted to grow to 1.56 billion by 2025. Hypertension often leads to diabetes mellitus that strongly puts the patients at an increased risk of cardiovascular, kidney, and/or atherosclerotic diseases. Hypertension has been identified as a major risk factor for the development of diabetes; patients with hypertension are at two-to-three-fold higher risk of developing diabetes than patients with normal blood pressure (BP). Causes for the increase in hypertension and diabetes are not well understood, environmental factors (e.g., exposure to environmental toxicants like heavy metals, organic solvents, pesticides, alcohol, and urban lifestyle) have been postulated as one of the reasons contributing to hypertension and cardiovascular diseases (CVD). The mechanism of action(s) of these toxicants in developing hypertension and CVDs is not well defined. Research studies have linked hypertension with the chronic consumption of alcohol and exposure to metals like lead, mercury, and arsenic have also been linked to hypertension and CVD. Workers chronically exposed to styrene have a higher incidence of CVD. Recent studies have demonstrated that exposure to particulate matter (PM) in diesel exhaust and urban air contributes to increased CVD and mortality. In this review, we have imparted the role of environmental toxicants such as heavy metals, organic pollutants, PM, alcohol, and some drugs in hypertension and CVD along with possible mechanisms and limitations in extrapolating animal data to humans.

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Rising incidence of hypertension may be linked to chronic exposure with environmental toxicants.

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Urban lifestyle and alcohol intake may be responsible for increased incidence of hypertension among urbanites.

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Exposure with organic solvent, heavy metals and pesticides could also be contributing to the rise in blood pressure.

Clinical and Molecular Perspectives of Monogenic Hypertension

Advances in molecular research techniques have enabled a new frontier in discerning the mechanisms responsible for monogenic diseases. In this review, we discuss the current research on the molecular pathways governing blood pressure disorders with a Mendelian inheritance pattern, each presenting with a unique pathophysiology. Glucocorticoid Remediable Aldosteronism (GRA) and Apparent Mineralocorticoid Excess (AME) are caused by mutations in regulatory enzymes that induce increased production of mineralocorticoids or inhibit degradation of glucocorticoids, respectively. Geller syndrome is due to a point mutation in the hormone responsive element of the promotor for the mineralocorticoid receptor, rendering the receptor susceptible to activation by progesterone, leading to hypertension during pregnancy. Pseudohypoaldosteronism type II (PHA-II), also known as Gordon's syndrome or familial hyperkalemic hypertension, is a more variable disorder typically characterized by hypertension, high plasma potassium and metabolic acidosis. Mutations in a variety of intracellular enzymes that lead to enhanced sodium reabsorption have been identified. In contrast, hypertension in Liddle's syndrome, which results from mutations in the Epithelial sodium Channel (ENaC), is associated with low plasma potassium and metabolic alkalosis. In Liddle's syndrome, truncation of one the ENaC protein subunits removes a binding site necessary protein for ubiquitination and degradation, thereby promoting accumulation along the apical membrane and enhanced sodium reabsorption. The myriad effects due to mutation in phosphodiesterase 3A (PDE3A) lead to severe hypertension underlying sodium-independent autosomal dominant hypertension with brachydactyly. How mutations in PDE3A result in the phenotypic features of this disorder are discussed. Understanding the pathologies of these monogenic hypertensive disorders may provide insight into the causes of the more prevalent essential hypertension and new avenues to unravel the complexities of blood pressure regulation.

Male Gender Identity and Reversible Hypokalemic Hypertension in a 46,XX Child with 11-Beta-Hydroxylase Deficiency Congenital Adrenal Hyperplasia

Steroid 11-beta-hydroxylase deficiency is a relatively rare form of congenital adrenal hyperplasia (CAH). We describe the case of a 46,XX child, reared as a male, who first presented to us at the age of three years with features of peripheral precocity and hypokalemic hypertension. Based on the clinical and biochemical profile, a diagnosis of 11-beta-hydroxylase deficiency CAH was established, and physiological glucocorticoid replacement was begun. Both hypertension and hypokalemia improved with glucocorticoid supplementation, and at eight years of age, antihypertensives were successfully withdrawn. Regression of left ventricular hypertrophy was also noted at this time. In keeping with the male gender identity, the child underwent hysterectomy, oopherectomy and breast reduction surgery at 13 years of age. We conclude that both hypertension and end-organ damage due to 11-beta-hydroxylase CAH may get reversed following optimal glucocorticoid treatment. Detailed genital examination at birth may help in early diagnosis of this rare disorder, thereby preventing the deleterious consequences of longstanding mineralocorticoid excess.