Increased Arterial Blood Pressure and Vascular Remodeling in Mice Lacking Salt-Inducible Kinase 1 (SIK1)

Rationale:

In human genetic studies a single nucleotide polymorphism within the salt-inducible kinase 1 ( SIK1 ) gene was associated with hypertension. Lower SIK1 activity in vascular smooth muscle cells (VSMCs) leads to decreased sodium-potassium ATPase activity, which associates with increased vascular tone. Also, SIK1 participates in a negative feedback mechanism on the transforming growth factor-β1 signaling and downregulation of SIK1 induces the expression of extracellular matrix remodeling genes.

Objective:

To evaluate whether reduced expression/activity of SIK1 alone or in combination with elevated salt intake could modify the structure and function of the vasculature, leading to higher blood pressure.

Methods and Results:

SIK1 knockout ( sik1 −/− ) and wild-type ( sik1 +/+ ) mice were challenged to a normal- or chronic high-salt intake (1% NaCl). Under normal-salt conditions, the sik1 −/− mice showed increased collagen deposition in the aorta but similar blood pressure compared with the sik1 +/+ mice. During high-salt intake, the sik1 +/+ mice exhibited an increase in SIK1 expression in the VSMCs layer of the aorta, whereas the sik1 −/− mice exhibited upregulated transforming growth factor-β1 signaling and increased expression of endothelin-1 and genes involved in VSMC contraction, higher systolic blood pressure, and signs of cardiac hypertrophy. In vitro knockdown of SIK1 induced upregulation of collagen in aortic adventitial fibroblasts and enhanced the expression of contractile markers and of endothelin-1 in VSMCs.

Conclusions:

Vascular SIK1 activation might represent a novel mechanism involved in the prevention of high blood pressure development triggered by high-salt intake through the modulation of the contractile phenotype of VSMCs via transforming growth factor-β1-signaling inhibition.

Pharmacological profile of opicapone, a third-generation nitrocatechol catechol-O-methyl transferase inhibitor, in the rat

BACKGROUND AND PURPOSE

Catechol-O-methyltransferase (COMT) is an important target in the levodopa treatment of Parkinson's disease; however, the inhibitors available have problems, and not all patients benefit from their efficacy. Opicapone was developed to overcome those limitations. In this study, opicapone's pharmacological properties were evaluated as well as its potential cytotoxic effects.

EXPERIMENTAL APPROACH

The pharmacodynamic effects of opicapone were explored by evaluating rat COMT activity and levodopa pharmacokinetics, in the periphery through microdialysis and in whole brain. The potential cytotoxicity risk of opicapone was explored in human hepatocytes by assessing cellular ATP content and mitochondrial membrane potential.

KEY RESULTS

Opicapone inhibited rat peripheral COMT with ED50 values below 1.4 mg⋅kg(-1) up to 6 h post-administration. The effect was sustained over the first 8 h and by 24 h COMT had not returned to control values. A single administration of opicapone resulted in increased and sustained plasma levodopa levels with a concomitant reduction in 3-O-methyldopa from 2 h up to 24 h post-administration, while tolcapone produced significant effects only at 2 h post-administration. The effects of opicapone on brain catecholamines after levodopa administration were sustained up to 24 h post-administration. Opicapone was also the least potent compound in decreasing both the mitochondrial membrane potential and the ATP content in human primary hepatocytes after a 24 h incubation period.

CONCLUSIONS AND IMPLICATIONS

Opicapone has a prolonged inhibitory effect on peripheral COMT, which extends the bioavailability of levodopa, without inducing toxicity. Thus, it exhibits some improved properties compared to the currently available COMT inhibitors.

Abstract 565: Genome-wide miRNA Expression Profiling and OPLS Discriminant Analysis in Hypertension and Cardiac Disease

MicroRNAs (miRNAs) are regulators of gene expression and play a key role in the pathophysiology of various disease processes, namely cardiovascular disease. This study aimed at the identification of the miRNA expression pattern of peripheral blood mononuclear cells derived from hypertensive subjects (HT) and non-hypertensive subjects with cardiac disease (CD) using a genome-wide approach. Furthermore, we explored the potential of orthogonal partial least squares-discrimination analysis (OPLS-DA) to analyze miRNA expression data. The homogeneity of the population was assessed with Principal Component Analysis (PCA) and verified by the clear separation of the three groups on the basis of the miRNA expression levels. Moreover, local PCA of HT group indicates the splitting of this group in two distinct subgroups. This distinction correlates with two subject’s characteristics (smoking habits and history of myocardial infarction) that are closest to the CD group. OPLS-DA analysis confirms the separation of three groups and identified the most important miRNA to discrimination between groups. Among the most influential miRNA to the positive differentiation of HT from CD and control, several of them are relevant to endothelial dysfunction. On the other hand, miRNAs associated with angiogenesis positively differentiate CD from HT and control. Mir-186, a regulator of myogenin, is the most important miRNA to discriminate HT from CD. These results provide evidence of altered miRNA profile in hypertensives and cardiac disease and demonstrate that PCA and OPLS-DA are very useful and robust tools to analyze how different miRNAs contribute to the separations of groups and to find interesting patterns within the multidimensional data.

Abstract 526: Blood Pressure in the SHR Following Renal Denervation or Etamicastat, a Novel Dopamine-β-Hydroxylase Inhibitor

Overactivity of the sympathetic nervous system plays an important role in the development and progression of hypertension. Catheter-based renal nerve ablation for treatment of drug-resistant hypertension has been recently developed. An alternative strategy for modulation of sympathetic nerve function is to reduce the biosynthesis of norepinephrine (NE) via inhibition of dopamine β-hydroxylase (DβH), the enzyme that catalysis the conversion of dopamine to NE in sympathetic nerves.

Renal denervation (RDN) was performed in spontaneously hypertensive rats (SHR) to evaluate the effect of RDN on NE levels and blood pressure throughout a 28-day period. Chronic oral treatment with the peripheral selective DβH inhibitor etamicastat (30 mg/kg/day) was performed in another cohort of SHR.

RDN and chronic oral treatment with etamicastat did not affect renal function, as assessed by urinary protein, creatinine and urea levels. RDN significantly decreased mean arterial blood pressure (MAP, in mm Hg) 7 days post-surgery (139±6, P<0.01) versus baseline values (158±6). A gradual MAP return to high baseline levels was observed overtime; 139±7 at day 14, 151±12, at day 21 and 155±12 at day 28 after RDN. Treatment with etamicastat decreased baseline MAP (150±5) in a sustained and significant (P<0.01) manner at all-time points: 141±5 at day 7, 139±5 at day 14, 138±5 at day 21 and 143±5 at day 28. At day 28, NE levels (in pmol/mg tissue) in renal tissue were significantly decreased in both RDN (0.12±0.08, P=0.001) and etamicastat-treated group (0.48±0.04, P=0.01) as compared to vehicle group (0.88±0.13). On the other hand, left ventricle NE levels were decreased only after treatment with etamicastat (1.24±0.12, P=0.04) but not in the RDN group (2.53±0.24, P=0.9) when compared to controls (2.59±0.58).

It is concluded that RDN produces transitory decreases in MAP, whereas prolonged down regulation of sympathetic drive with the DβH inhibitor etamicastat results in sustained decreases in MAP.

Abstract 505: Effects of Etamicastat, a Selective Peripheral Dopamine-β-Hydroxylase Inhibitor, Upon Stress-induced Changes in Blood Pressure in the SHR

Stressors induce an overactivation of the sympathetic nervous system (SNS) that triggers several changes in the body as a response to stress. These changes include vasoconstriction and increase in heart rate, which results in raised blood pressure (BP). Etamicastat is a selective dopamine-β-hydroxylase (DβH) inhibitor that decreases norepinephrine levels in peripheral sympathetically innervated tissues.

Cardiovascular parameters were measured after a single oral administration of etamicastat (30 mg/kg) 9 h post-administration in male spontaneously hypertensive rats (SHR) by radio-telemetry or tail-cuff recording. Telemetered recording was performed in both restrained and unrestrained animals.

Etamicastat treatment had no effect on heart rate (HR, beats/min) in any recording method. HR measured in unrestrained SHR instrumented with radio-telemetry probes (305±5) consistently yielded HR values significantly lower than restrained animals (362±11) or those recorded by tail-cuff (393±7). On the other hand, single-dose oral etamicastat treatment decrease in mean arterial pressure (MAP, mm Hg) was -14.0±2.0 from 153.3±4.0 in telemetered unrestrained animals, -26.1±5.1 from 182.8±6.4 in telemetry-implanted restrained SHR and -47.9±7.0 from 183.4±9.5 recorded by tail-cuff method. In addition, a power spectral analysis was performed to evaluate BP variability (BPV), in SHR implanted with radio-telemetry probes, at high frequency (HF: 1-2 Hz), low frequency (LF: 0.2-0.6 Hz) and very low frequency (VLF: 0.02-0.2 Hz). The stressor (i.e., cage restrainement) increased the ratio LF/HF-BPV in untreated SHR from 5.23±1.24 to 10.03±1.75, which results from the activation of the SNS. Treatment with etamicastat decreased the ratio LF/HF-BPV in stressed SHR from 10.03±1.75 to 4.46±0.68 and in non-stressed SHR from 5.23±1.24 to 2.23±0.39.

In conclusion, etamicastat treatment reduces (1) high BP in SHR, (2) the stress-induced increase in SNS drive and (3) the stress-induced increase in BP.

Abstract 504: Cardiac Safety Profile of Etamicastat, a Novel Peripheral Selective Dopamine-ß-Hydroxylase Inhibitor, in the Dog

Etamicastat, a peripheral reversible dopamine-ß-hydroxylase inhibitor, blocked the hERG current amplitude with an IC50 value of 35.4 μg/ml in HEK 293 cells. At 0.3 and 3 μg/ml, etamicastat had no effects on the action potential (AP) in dog Purkinje fibers. At 30 μg/ml, etamicastat significantly affected resting membrane potential (+4%), AP amplitude (-4%), AP duration at 60% (-14%) and AP duration at 90% (+5%) repolarization, and AP triangulation (+79%). In the telemetered conscious dog, etamicastat (up to 20 mg/kg) had no effects on arterial blood pressure, heart rate and the PR interval. At 10 and 20 mg/kg, the QTc interval was slightly prolonged (8 to 9% max, P < 0.05). No arrhythmia or other changes in the morphology of the ECG were observed. The maximum observed plasma concentrations (Cmax) of etamicastat (i.e. 3h post administration) were 1.4 and 3.7 μg/ml at 10 and 20 mg/kg, respectively. No deleterious effects, including ECG disturbance were observed in male and female dogs dosed by gavage with etamicastat (up to 20 mg/kg/day) for 28 days. Mean plasma Cmax etamicastat levels ranged between 2.4 and 6.3 μg/ml on Day 1 and Day 28 of treatment, respectively. It is concluded that the blockade of the delayed rectifier potassium channels by etamicastat together with the QTc interval prolongation observed in conscious dogs can be considered as modest with respect to the measured plasmatic concentrations. These findings suggest that etamicastat is not likely to prolong the QT interval at therapeutic doses (~ 0.2 μg/ml).

Human disposition, metabolism and excretion of etamicastat, a reversible, peripherally selective dopamine β-hydroxylase inhibitor

AIMS

Etamicastat is a reversible dopamine-β-hydroxylase inhibitor that decreases noradrenaline levels in sympathetically innervated tissues and slows down sympathetic nervous system drive. In this study, the disposition, metabolism and excretion of etamicastat were evaluated following [(14)C]-etamicastat dosing.

METHODS

Healthy Caucasian males (n = 4) were enrolled in this single-dose, open-label study. Subjects were administered 600 mg of unlabelled etamicastat and 98 µCi weighing 0.623 mg [(14)C]-etamicastat. Blood samples, urine and faeces were collected to characterize the disposition, excretion and metabolites of etamicastat.

RESULTS

Eleven days after administration, 94.0% of the administered radioactivity had been excreted; 33.3 and 58.5% of the administered dose was found in the faeces and urine, respectively. Renal excretion of unchanged etamicastat and its N-acetylated metabolite (BIA 5-961) accounted for 20.0 and 10.7% of the dose, respectively. Etamicastat and BIA 5-961 accounted for most of the circulating radioactivity, with a BIA 5-961/etamicastat ratio that was highly variable both for the maximal plasma concentration (19.68-226.28%) and for the area under the plasma concentration-time curve from time zero to the last sampling time at which the concentration was above the limit of quantification (15.82- 281.71%). Alongside N-acetylation, metabolism of etamicastat also occurs through oxidative deamination of the aminoethyl moiety, alkyl oxidation, desulfation and glucuronidation.

CONCLUSIONS

Etamicastat is rapidly absorbed, primarily excreted via urine, and its biotransformation occurs mainly via N-acetylation (N-acetyltransferase type 2), although glucuronidation, oxidation, oxidative deamination and desulfation also take place.

Lack of salt-inducible kinase 2 (SIK2) prevents the development of cardiac hypertrophy in response to chronic high-salt intake

Cardiac left ventricle hypertrophy (LVH) constitutes a major risk factor for heart failure. Although LVH is most commonly caused by chronic elevation in arterial blood pressure, reduction of blood pressure to normal levels does not always result in regression of LVH, suggesting that additional factors contribute to the development of this pathology. We tested whether genetic preconditions associated with the imbalance in sodium homeostasis could trigger the development of LVH without concomitant increases in blood pressure. The results showed that the presence of a hypertensive variant of α-adducin gene in Milan rats (before they become hypertensive) resulted in elevated expression of genes associated with LVH, and of salt-inducible kinase 2 (SIK2) in the left ventricle (LV). Moreover, the mRNA expression levels of SIK2, α-adducin, and several markers of cardiac hypertrophy were positively correlated in tissue biopsies obtained from human hearts. In addition, we found in cardiac myocytes that α-adducin regulates the expression of SIK2, which in turn mediates the effects of adducin on hypertrophy markers gene activation. Furthermore, evidence that SIK2 is critical for the development of LVH in response to chronic high salt diet (HS) was obtained in mice with ablation of the sik2 gene. Increases in the expression of genes associated with LVH, as well as increases in LV wall thickness upon HS, occurred only in sik2^+/+ but not in sik2^−/− mice. Thus LVH triggered by HS or the presence of a genetic variant of α-adducin requires SIK2 and is independent of elevated blood pressure. Inhibitors of SIK2 may constitute part of a novel therapeutic regimen aimed at prevention/regression of LVH.

The effects of eslicarbazepine on persistent Na⁺ current and the role of the Na⁺ channel β subunits

Eslicarbazepine is the major active metabolite of eslicarbazepine acetate, a once-daily antiepileptic drug approved in Europe as adjunctive therapy for refractory partial-onset seizures in adults. This study was aimed to determine the effects of eslicarbazepine on persistent Na(+) currents (INaP) and the role of β subunits in modulating these effects. To study the role of β subunits of the Na(+) channel we used a mouse line genetically lacking either the β1 or β2 subunit, encoded by the SCN1B or SCN2B gene, respectively. Whole cell patch-clamp recordings were performed on CA1 neurons in hippocampal slices under control conditions and application of 300 μM eslicarbazepine. We examined INaP in acutely isolated CA1 neurons and repetitive firing in hippocampal slices of mice lacking β subunits and corresponding wild-type littermates. We found that eslicarbazepine caused a significant reduction of maximal INaP conductance and an efficient reduction of the firing rate in wild-type mice. We have shown previously a paradoxical increase of conductance of INaP caused by carbamazepine in mice lacking β1 subunits in the subthreshold range, leading to a failure in affecting neuronal firing (Uebachs et al., 2010). In contrast, eslicarbazepine did not cause this paradoxical effect on INaP in SCN1B null mice. Consequently, the effects of eslicarbazepine on repetitive firing were maintained in these animals. These results indicate that eslicarbazepine exerts effects on INaP similar to those known for carbamazepine. However, in animals lacking the β1 Na(+) channel subunit these effects are maintained. Therefore, eslicarbazepine potentially overcomes a previously described putative mechanism of resistance to established Na(+) channel acting antiepileptic drugs.

Brain and peripheral pharmacokinetics of levodopa in the cynomolgus monkey following administration of opicapone, a third generation nitrocatechol COMT inhibitor

OBJECTIVE

The present study aimed at evaluating the effect of opicapone, a third generation nitrocatechol catechol-O-methyltransferase (COMT) inhibitor, on the systemic and central bioavailability of 3,4-dihydroxy-l-phenylalanine (levodopa) and related metabolites in the cynomolgus monkey.

METHODS

Four monkeys, implanted with guiding cannulas for microdialysis probes, in the substantia nigra, dorsal striatum and prefrontal cortex, were randomized in two groups that received, in a crossover design, vehicle or 100 mg/kg opicapone for 14 days. Twenty-three hours after last administration of vehicle or opicapone, animals were challenged with levodopa/benserazide (12/3 mg/kg). Extracellular dialysate and blood samples were collected over 360 min (at 30 min intervals) for the assays of catecholamine and COMT activity.

RESULTS

Opicapone increased levodopa systemic exposure by 2-fold not changing Cmax values and reduced both 3-O-methyldopa (3-OMD) exposure and Cmax values by 5-fold. These changes were accompanied by ∼76-84% reduction in erythrocyte COMT activity. In dorsal striatum and substantia nigra, opicapone increased levodopa exposure by 1.7- and 1.4-fold, respectively, reducing 3-OMD exposure by 5- and 7-fold respectively. DOPAC exposure was increased by 4-fold in the substantia nigra. In the prefrontal cortex, opicapone increased levodopa exposure and reduced 3-OMD levels by 2.3- and 2.4-fold, respectively.

CONCLUSIONS

Opicapone behaved as long-acting COMT inhibitor that markedly increased systemic and central levodopa bioavailability. Opicapone is a strong candidate to fill the unmet need for COMT inhibitors that lead to more sustained levodopa levels in Parkinson's disease patients.

Abstract 204: Sodium Sensing Network in Hypertension-Induced Cardiac Hypertrophy

Hypertension is related to alterations of sodium homeostasis that promote abnormal accumulation of water in the intravascular compartment leading to blood pressure elevation. This process can been associated with increased heart mass resulting in cardiac hypertrophy. At cellular level, the concentration and active transport of Na+ is regulated by Na+,K+-ATPase enzyme (NK). In vitro studies have shown a correlation between high blood pressure, NK and SIK activities. Increases in intracellular Na+ are paralleled by elevations in intracellular Ca2+ via NCX1, leading to the activation of SIK1 by a Ca2+/calmodulin-dependent kinase. Activation of SIK1 results in the dephosphorylation of the NK α-subunit and an increase in its catalytic activity. Accordingly, the aim of the present study was to evaluate the cardiac Na+ sensing network changes associated with hypertension in aging hypertensive rats. Systolic and diastolic blood pressures, determined by the tail-cuff method, were significantly higher in 3, 13 and 21-month old SHR than in age-matched WKY. In the SHR, ageing was associated with increases in cardiac mass, gene expression of hypertrophic (α-skeletal muscle actin and β-myosin heavy chain) markers as well as inflammatory cytokine (IL-6). The decreased expression of heart SIK isoforms, SIK1 and SIK3, was associated with downregulation of transcription factors Snail2, Zeb1, MFAT5c and KLF4, in 13 and 21-month old SHR. Cardiac α2-isoform of NK was found to be decreased in 21 month old SHR. Whereas, NKα1, NHE3 and NCX1 showed no differences between age-matched SHR and WKY. Na+-dependent ASCT2 and Na+-independent LAT1 amino acid transporter transcript levels of were significantly higher in 21 month old SHR than in WKY. In the aged SHR, cardiac hypertrophy was associated with dysregulation of several elements of the intracellular Na+ sensing network. Downregulation of SIK1 and transcription factors is correlated with expression of NKα2, suggesting impaired sodium handling. It is proposed that, cardiac hypertrophy is not exclusively the consequence of mechanical stress but also of other factors associated with elevated blood pressure such as abnormal cell sodium homeostasis.Supported by grant PIC/IC/83204/2007.