Quantification of isradipine in human plasma using LC-MS/MS for pharmacokinetic and bioequivalence study

Novel protocol for multiple-dose oral administration of the L-type Ca2+ channel blocker isradipine in mice: A dose-finding pharmacokinetic study

Studies in genetically modified animals and human genetics have recently provided new insight into the role of voltage-gated L-type Ca2+ channels in human disease. Therefore, the inhibition of L-type Ca2+ channels in vivo in wildtype and mutant mice by potent dihydropyridine (DHP) Ca2+ channel blockers serves as an important pharmacological tool. These drugs have a short plasma half-life in humans and especially in rodents and show high first-pass metabolism upon oral application. In the vast majority of in vivo studies, they have therefore been delivered through parenteral routes, mostly subcutaneously or intraperitoneally. High peak plasma concentrations of DHPs cause side effects, evident as DHP-induced aversive behaviors confounding the interpretation of behavioral readouts. Nevertheless, pharmacokinetic data measuring the exposure achieved with these applications are sparse. Moreover, parenteral injections require animal handling and can be associated with pain, discomfort and stress which could influence a variety of physiological processes, behavioral and other functional readouts. Here, we describe a noninvasive oral application of the DHP isradipine by training mice to quickly consume small volumes of flavored yogurt that can serve as drug vehicle. This procedure does not require animal handling, allows repeated drug application over several days and reproducibly achieves peak plasma concentrations over a wide range previously shown to be well-tolerated in humans. This protocol should facilitate ongoing nonclinical studies in mice exploring new indications for DHP Ca2+ channel blockers.

A novel method to estimate the absorption rate constant for two-compartment model fitted drugs without intravenous pharmacokinetic data

The in vivo performances of most drugs after extravascular administration are fitted well with the two-compartment pharmacokinetic (PK) model, but the estimation of absorption rate constant (k_a) for these drugs becomes difficult during unavailability of intravenous PK data. Herein, we developed a novel method, called the direct method, for estimating the k_a values of drugs without using intravenous PK data, by proposing a new PK parameter, namely, maximum apparent rate constant of disposition (k_max). The accuracy of the direct method in k_a estimation was determined using the setting parameters (k₁₂, k₂₁, and k₁₀ values at high, medium, and low levels, respectively) and clinical data. The results showed that the absolute relative error of k_a estimated using the direct method was significantly lower than that obtained using both the Loo-Riegelman method and the statistical moment method for the setting parameters. Human PK studies of telmisartan, candesartan cilexetil, and tenofovir disoproxil fumarate indicated that the k_a values of these drugs were accurately estimated using the direct method based on good correlations between the k_a values and other PK parameters that reflected the absorption properties of drugs in vivo (T_max, C_max, and C_max/AUC_0-t). This novel method can be applied in situations where intravenous PK data cannot be obtained and is expected to provide valuable support for PK evaluation and in vitro-in vivo correlation establishment.

CACNA1D-Related Channelopathies: From Hypertension to Autism

Tightly controlled Ca²⁺ influx through voltage-gated Ca²⁺ channels (Cavs) is indispensable for proper physiological function. Thus, it is not surprising that Cav loss and/or gain of function have been implicated in human pathology. Deficiency of Cav1.3 L-type Ca²⁺ channels (LTCCs) causes deafness and bradycardia, whereas several genetic variants of CACNA1D, the gene encoding the pore-forming α1 subunit of Cav1.3, have been linked to various disease phenotypes, such as hypertension, congenital hypoglycemia, or autism. These variants include not only common polymorphisms associated with an increased disease risk, but also rare de novo missense variants conferring high risk. This review provides a concise summary of disease-associated CACNA1D variants, whereas the main focus lies on de novo germline variants found in individuals with a neurodevelopmental disorder of variable severity. Electrophysiological recordings revealed activity-enhancing gating changes induced by these de novo variants, and tools to predict their pathogenicity and to study the resulting pathophysiological consequences will be discussed. Despite the low number of affected patients, potential phenotype-genotype correlations and factors that could impact the severity of symptoms will be covered. Since increased channel activity is assumed as the disease-underlying mechanism, pharmacological inhibition could be a treatment option. In the absence of Cav1.3-selective blockers, dihydropyridine LTCC inhibitors clinically approved for the treatment of hypertension may be used for personalized off-label trials. Findings from in vitro studies and treatment attempts in some of the patients seem promising as outlined. Taken together, due to advances in diagnostic sequencing techniques the number of reported CACNA1D variants in human diseases is constantly rising. Evidence from in silico, in vitro, and in vivo disease models can help to predict the pathogenic potential of such variants and to guide diagnosis and treatment in the clinical practice when confronted with patients harboring CACNA1D variants.

Questioning the renoprotective role of L-type calcium channel blockers in chronic kidney disease using physiological modeling

Chronic kidney disease (CKD) is characterized by the progressive functional loss of nephrons and hypertension (HTN). Some antihypertensive regimens attenuate the progression of CKD (blockers of the renin-angiotensin system). Although studies have suggested that calcium channel blocker (CCB) therapy mitigates the decline in renal function in humans with essential HTN, there are few long-term clinical studies that have determined the impact of CCBs in patients with hypertensive CKD. Dihydropyridine (DHP) or L-type CCBs preferentially vasodilate the afferent arteriole and have been associated with glomerular HTN and increases in proteinuria in animal models with low renal function. Small clinical studies in vulnerable populations with renal disease such as African Americans, children, and diabetics have also suggested that DHP CCBs exacerbate glomerular injury, which questions the renoprotective effect of this class of antihypertensive drug. We used an established integrative mathematical model of human physiology, HumMod, to test the hypothesis that DHP CCB therapy exacerbates pressure-induced glomerular injury in hypertensive CKD. Over a simulation of 3 yr, CCB therapy reduced mean blood pressure by 14-16 mmHg in HTN both with and without CKD. Both impaired tubuloglomerular feedback and low baseline renal function exacerbated glomerular pressure, glomerulosclerosis, and the decline in renal function during L-type CCB treatment. However, simulating CCB therapy that inhibited both L- and T-type calcium channels increased efferent arteriolar vasodilation and alleviated glomerular damage. These simulations support the evidence that DHP (L-type) CCBs potentiate glomerular HTN during CKD and suggest that T/L-type CCBs are valuable in proteinuric renal disease treatment.NEW & NOTEWORTHY Our physiological model replicates clinical trial results and provides unique insights into possible mechanisms that play a role in glomerular injury and hypertensive kidney disease progression during chronic CCB therapy. Specifically, these simulations predict the temporal changes in renal function with CCB treatment and demonstrate important roles for tubuloglomerular feedback and efferent arteriolar conductance in the control of chronic kidney disease progression.

The Potential of L-Type Calcium Channels as a Drug Target for Neuroprotective Therapy in Parkinson's Disease

The motor symptoms of Parkinson's disease (PD) mainly arise from degeneration of dopamine neurons within the substantia nigra. As no disease-modifying PD therapies are available, and side effects limit long-term benefits of current symptomatic therapies, novel treatment approaches are needed. The ongoing phase III clinical study STEADY-PD is investigating the potential of the dihydropyridine isradipine, an L-type Ca²⁺ channel (LTCC) blocker, for neuroprotective PD therapy. Here we review the clinical and preclinical rationale for this trial and discuss potential reasons for the ambiguous outcomes of in vivo animal model studies that address PD-protective dihydropyridine effects. We summarize current views about the roles of Cav1.2 and Cav1.3 LTCC isoforms for substantia nigra neuron function, and their high vulnerability to degenerative stressors, and for PD pathophysiology. We discuss different dihydropyridine sensitivities of LTCC isoforms in view of their potential as drug targets for PD neuroprotection, and we conclude by considering how these aspects could guide further drug development.

Ca2+ Channels in Anterior Pituitary Somatotrophs: A Therapeutic Perspective

Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) plays a key role in GH secretion. In this review, we summarize the current state of knowledge regarding the physiology and molecular machinery of VGCCs in pituitary somatotrophs. We next discuss the possible involvement of Ca2+ channelopathies in pituitary disease and the potential use of Ca2+ channel blockers to treat pituitary disease. Various types of VGCCs exist in pituitary cells. However, because L-type Ca2+ channels (LTCCs) contribute the major component to Ca2+ influx in somatotrophs, lactotrophs, and corticotrophs, we focused on these channels. An increasing number of studies in recent years have linked genetic missense mutations in LTCCs to diseases of the human cardiovascular, nervous, and endocrine systems. These disease-associated genetic mutations occur at homologous functional positions (activation gates) in LTCCs. Thus, it is plausible that similar homologous missense mutations in pituitary LTCCs can cause abnormal hormone secretion and underlying pituitary disorders. The existence of LTCCs in pituitary cells opens questions about their sensitivity to dihydropyridines, a group of selective LTCC blockers. The dihydropyridine sensitivity of pituitary cells, as with any other excitable cell, depends primarily on two parameters: the pattern of their electrical activity and the dihydropyridine sensitivity of their LTCC isoforms. These two parameters are discussed in detail in relation to somatotrophs. These discussions are also relevant to lactotrophs and corticotrophs. High dihydropyridine sensitivity may facilitate their use as drugs to treat pituitary oversecretion disorders such as acromegaly, hyperprolactinemia, and Cushing disease.

Systemic isradipine treatment diminishes calcium-dependent mitochondrial oxidant stress

The ability of the Cav1 channel inhibitor isradipine to slow the loss of substantia nigra pars compacta (SNc) dopaminergic (DA) neurons and the progression of Parkinson's disease (PD) is being tested in a phase 3 human clinical trial. But it is unclear whether and how chronic isradipine treatment will benefit SNc DA neurons in vivo. To pursue this question, isradipine was given systemically to mice at doses that achieved low nanomolar concentrations in plasma, near those achieved in patients. This treatment diminished cytosolic Ca2+ oscillations in SNc DA neurons without altering autonomous spiking or expression of Ca2+ channels, an effect mimicked by selectively knocking down expression of Cav1.3 channel subunits. Treatment also lowered mitochondrial oxidant stress, reduced a high basal rate of mitophagy, and normalized mitochondrial mass - demonstrating that Cav1 channels drive mitochondrial oxidant stress and turnover in vivo. Thus, chronic isradipine treatment remodeled SNc DA neurons in a way that should not only diminish their vulnerability to mitochondrial challenges, but to autophagic stress as well.

Lower Affinity of Isradipine for L-Type Ca2+ Channels during Substantia Nigra Dopamine Neuron-Like Activity: Implications for Neuroprotection in Parkinson's Disease

Ca2+-influx through L-type Ca2+-channels (LTCCs) is associated with activity-related stressful oscillations of Ca2+ levels within dopaminergic (DA) neurons in the substantia nigra (SN), which may contribute to their selective degeneration in Parkinson's disease (PD). LTCC blockers were neuroprotective in mouse neurotoxin models of PD, and isradipine is currently undergoing testing in a phase III clinical trial in early PD. We report no evidence for neuroprotection by in vivo pretreatment with therapeutically relevant isradipine plasma levels, or Cav1.3 LTCC deficiency in 6-OHDA-treated male mice. To explain this finding, we investigated the pharmacological properties of human LTCCs during SN DA-like and arterial smooth muscle (aSM)-like activity patterns using whole-cell patch-clamp recordings in HEK293 cells (Cav1.2 α1-subunit, long and short Cav1.3 α1-subunit splice variants; β3/α2δ1). During SN DA-like pacemaking, only Cav1.3 variants conducted Ca2+ current (ICa) at subthreshold potentials between action potentials. SN DA-like burst activity increased integrated ICa during (Cav1.2 plus Cav1.3) and after (Cav1.3) the burst. Isradipine inhibition was splice variant and isoform dependent, with a 5- to 11-fold lower sensitivity to Cav1.3 variants during SN DA-like pacemaking compared with Cav1.2 during aSM-like activity. Supratherapeutic isradipine concentrations reduced the pacemaker precision of adult mouse SN DA neurons but did not affect their somatic Ca2+ oscillations. Our data predict that Cav1.2 and Cav1.3 splice variants contribute differentially to Ca2+ load in SN DA neurons, with prominent Cav1.3-mediated ICa between action potentials and after bursts. The failure of therapeutically relevant isradipine levels to protect SN DA neurons can be explained by weaker state-dependent inhibition of SN DA LTCCs compared with aSM Cav1.2.SIGNIFICANCE STATEMENT The high vulnerability of dopamine (DA) neurons in the substantia nigra (SN) to neurodegenerative stressors causes Parkinson's disease (PD). Ca2+ influx through voltage-gated L-type Ca2+ channels (LTCCs), in particular Cav1.3, appears to contribute to this vulnerability, and the LTCC inhibitor isradipine is currently being tested as a neuroprotective agent for PD in a phase III clinical trial. However, in our study isradipine plasma concentrations approved for therapy were not neuroprotective in a PD mouse model. We provide an explanation for this observation by demonstrating that during SN DA-like neuronal activity LTCCs are less sensitive to isradipine than Cav1.2 LTCCs in resistance blood vessels (mediating dose-limiting vasodilating effects) and even at supratherapeutic concentrations isradipine fails to reduce somatic Ca2+ oscillations of SN DA neurons.

L-type calcium channels as drug targets in CNS disorders

L-type calcium channels are present in most electrically excitable cells and are needed for proper brain, muscle, endocrine and sensory function. There is accumulating evidence for their involvement in brain diseases such as Parkinson disease, febrile seizures and neuropsychiatric disorders. Pharmacological inhibition of brain L-type channel isoforms, Cav1.2 and Cav1.3, may therefore be of therapeutic value. Organic calcium channels blockers are clinically used since decades for the treatment of hypertension, cardiac ischemia, and arrhythmias with a well-known and excellent safety profile. This pharmacological benefit is mainly mediated by the inhibition of Cav1.2 channels in the cardiovascular system. Despite their different biophysical properties and physiological functions, both brain channel isoforms are similarly inhibited by existing calcium channel blockers. In this review we will discuss evidence for altered L-type channel activity in human brain pathologies, new therapeutic implications of existing blockers and the rationale and current efforts to develop Cav1.3-selective compounds.

Pharmacokinetic properties of isradipine after single-dose and multiple-dose oral administration in Chinese volunteers: a randomized, open-label, parallel-group phase I study

Isradipine could be used for the treatment of high blood pressure or Parkinsonism, yet the study on pharmacokinetics (PK) of isradipine is lacking in the Chinese population. The current study aims to assess the dose proportionality, pharmacokinetics and gender effect of isradipine following oral single and multiple doses in Chinese subjects. A randomized, open-label, parallel-group trial was conducted in 30 healthy Chinese volunteers. Subjects randomly received a single dose of 2.5, 5 or 10 mg, and multiple doses (2.5 mg) of isradipine. Blood samples were collected pre-dose (0 h) and 0.33, 0.67, 1, 1.5, 2, 3, 4, 6, 9, 12, 24, 36 and 48 h post-dose. Isradipine was rapidly absorbed with the time to maximum concentration <1.27 h for all dosage groups. The maximum concentrations were 2.46, 5.34, 10.93 and 3.32 ng/mL and area under the concentration-time curve from time zero to the last time point (AUClast ) were 7.05, 12.58, 24.68 and 5.31 ng/ml · h for the 2.5, 5 and 10 mg single-dose and 2.5 mg multiple-dose groups, respectively. The half-life ranged from 5.76 to 7.94 h. The maximum concentration and AUC were found to increase linearly and dose-dependently for isradipine. No statistical gender differences were found. These findings indicated that the pharmacokinetic parameters of isradipine in Chinese population were dose-proportional and predictable over a range of 2.5-10 mg isradipine oral doses.

Calcium channel blocking as a therapeutic strategy for Alzheimer's disease: the case for isradipine

Alzheimer's disease is the most devastating neurodegenerative disorder in the elderly, yet treatment options are severely limited. The drug development effort to modify Alzheimer's disease pathology by intervention at beta amyloid production sites has been largely ineffective or inconclusive. The greatest challenge has been to identify and define downstream mechanisms reliably predictive of clinical symptoms. Beta amyloid accumulation leads to dysregulation of intracellular calcium by plasma membrane L-type calcium channels located on neuronal somatodendrites and axons in the hippocampus and cortex. Paradoxically, L-type calcium channel subtype Ca(v)1.2 also promotes synaptic plasticity and spatial memory. Increased intracellular calcium modulates amyloid precursor protein processing and affects multiple downstream pathways including increased hyperphosphorylated tau and suppression of autophagy. Isradipine is a Federal Drug Administration-approved dihydropyridine calcium channel blocker that binds selectively to Ca(v)1.2 in the hippocampus. Our studies have shown that isradipine in vitro attenuates beta amyloid oligomer toxicity by suppressing calcium influx into cytoplasm and by suppressing Ca(v)1.2 expression. We have previously shown that administration of isradipine to triple transgenic animal model for Alzheimer's disease was well-tolerated. Our results further suggest that isradipine became bioavailable, lowered tau burden, and improved autophagy function in the brain. A better understanding of brain pharmacokinetics of calcium channel blockers will be critical for designing new experiments with appropriate drug doses in any future clinical trials for Alzheimer's disease. This review highlights the importance of Ca(v)1.2 channel overexpression, the accumulation of hyperphosphorylated tau and suppression of autophagy in Alzheimer's disease and modulation of this pathway by isradipine.

A translational continuum of model systems for evaluating treatment strategies in Alzheimer's disease: isradipine as a candidate drug

A growing body of evidence supports the 'calcium hypothesis' of Alzheimer's disease (AD), which postulates that a variety of insults might disrupt the homeostatic regulation of neuronal calcium (Ca(2+)) in the brain, resulting in the progressive symptoms that typify the disease. However, despite ongoing efforts to develop new methods for testing therapeutic compounds that might be beneficial in AD, no single bioassay permits both rapid screening and in vivo validation of candidate drugs that target specific components of the Ca(2+) regulatory machinery. To address this issue, we have integrated four distinct model systems that provide complementary information about a trial compound: the human neuroblastoma MC65 line, which provides an in vitro model of amyloid toxicity; a transgenic Drosophila model, which develops age-dependent pathologies associated with AD; the 3×TgAD transgenic mouse, which recapitulates many of the neuropathological features that typify AD; and the embryonic nervous system of Manduca, which provides a novel in vivo assay for the acute effects of amyloid peptides on neuronal motility. To demonstrate the value of this 'translational suite' of bioassays, we focused on a set of clinically approved dihydropyridines (DHPs), a class of well-defined inhibitors of L-type calcium channels that have been suggested to be neuroprotective in AD. Among the DHPs tested in this study, we found that isradipine reduced the neurotoxic consequences of β-amyloid accumulation in all four model systems without inducing deleterious side effects. Our results provide new evidence in support of the Ca(2+) hypothesis of AD, and indicate that isradipine represents a promising drug for translation into clinical trials. In addition, these studies also demonstrate that this continuum of bioassays (representing different levels of complexity) provides an effective means of evaluating other candidate compounds that target specific components of the Ca(2+) regulatory machinery and that therefore might be beneficial in the treatment of AD.

Phytic acid as a potential treatment for alzheimer's pathology: evidence from animal and in vitro models

Alzheimer's disease (AD) causes progressive, age-dependent cortical and hippocampal dysfunction leading to abnormal intellectual capacity and memory. We propose a novel protective treatment for AD pathology with phytic acid (inositol hexakisphosphate), a phytochemical found in food grains and a key signaling molecule in mammalian cells. We evaluated the protective and beneficial effects of phytic acid against amyloid-β (Aβ) pathology in MC65 cells and the Tg2576 mouse model. In MC65 cells, 48-72-hour treatment with phytic acid provided complete protection against amyloid precursor protein-C-terminal fragment-induced cytotoxicity by attenuating levels of increased intracellular calcium, hydrogen peroxide, superoxide, Aβ oligomers, and moderately upregulated the expression of autophagy (beclin-1) protein. In a tolerance paradigm, wild type mice were treated with 2% phytic acid in drinking water for 70 days. Phytic acid was well tolerated. Ceruloplasmin activity, brain copper and iron levels, and brain superoxide dismutase and ATP levels were unaffected by the treatment. There was a significant increase in brain levels of cytochrome oxidase and a decrease in lipid peroxidation with phytic acid administration. In a treatment paradigm, 12-month old Tg2576 and wild type mice were treated with 2% phytic acid or vehicle for 6 months. Brain levels of copper, iron, and zinc were unaffected. The effects of phytic acid were modest on the expression of AβPP trafficking-associated protein AP180, autophagy-associated proteins (beclin-1, LC3B), sirtuin 1, the ratio of phosphorylated AMP-activated protein kinase (PAMPK) to AMPK, soluble Aβ1-40, and insoluble Aβ1-42. These results suggest that phytic acid may provide a viable treatment option for AD.

The L-type channel antagonist isradipine is neuroprotective in a mouse model of Parkinson's disease

The motor symptoms of Parkinson's disease (PD) are due to the progressive loss of dopamine (DA) neurons in substantia nigra pars compacta (SNc). Nothing is known to slow the progression of the disease, making the identification of potential neuroprotective agents of great clinical importance. Previous studies using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have shown that antagonism of L-type Ca2+ channels protects SNc DA neurons. However, this was not true in a 6-hydroxydopamine (6-OHDA) model. One potential explanation for this discrepancy is that protection in the 6-OHDA model requires greater antagonism of Cav1.3 L-type Ca2+ channels thought to underlie vulnerability and this was not achievable with the low affinity dihydropyridine (DHP) antagonist used. To test this hypothesis, the DHP with the highest affinity for Cav1.3L-type channels-isradipine-was systemically administered and then the DA toxin 6-OHDA injected intrastriatally. Twenty-five days later, neuroprotection and plasma concentration of isradipine were determined. This analysis revealed that isradipine produced a dose-dependent sparing of DA fibers and cell bodies at concentrations achievable in humans, suggesting that isradipine is a potentially viable neuroprotective agent for PD.

L-type voltage-gated calcium channel blockade with isradipine as a therapeutic strategy for Alzheimer's disease

There is strong evidence that intracellular calcium dysregulation plays an important pathological role in Alzheimer's disease, and specifically that beta amyloid may induce increases in intracellular calcium and lead to neuronal cell dysfunction and death. Here we investigated the feasibility of modifying Alzheimer's pathology with the L-type voltage-gated calcium channel blockers verapamil, diltiazem, isradipine and nimodipine. All four compounds protected MC65 neuroblastoma cells from amyloid beta protein precursor C-terminal fragment (APP CTF)-induced neurotoxicity. Isradipine was the most potent blocker, preventing APP CTF neurotoxicity at nanomolar concentrations. Intracellular beta amyloid expression was associated with increased expression of Cav 1.2 calcium channels and increased intracellular calcium influx from the extracellular space. Despite the cytoprotection afforded by calcium channel blockers, amyloid beta oligomer formation was not suppressed. The mechanism of cell death in MC65 cells is appeared to be caspase-3 independent. With the goal of determining if there is sufficient experimental support to move forward with animal trials of isradipine, we determined its bioavailability in the triple transgenic mouse model of AD. Subcutaneous implantation of carrier-bound isradipine (3 μg/g/day) for 60 days resulted in nanomolar concentrations in both the plasma and brain. Taken together, our in vitro results support the theory that calcium blockers exert protective effects downstream of the effects of beta amyloid. Isradipine's neuroprotective effect at concentrations that are clinically relevant and achievable in vitro and in vivo suggests that this particular calcium blocking agent may have therapeutic value in the treatment of Alzheimer's disease.