Leukocyte cathepsin S is a potent regulator of both cell and matrix turnover in advanced atherosclerosis

OBJECTIVE

A dysbalance of proteases and their inhibitors is instrumental in remodeling of atherosclerotic plaques. One of the proteases implicated in matrix degradation is cathepsin-S (CatS). To address its role in advanced lesion composition, we generated chimeric LDLr(-/-) mice deficient in leukocyte CatS by transplantation with CatS(-/-)xLDLr(-/-) or with LDLr(-/-) bone marrow and administered a high-fat diet.

METHODS AND RESULTS

No difference in aortic root lesion size could be detected between CatS(+/+) and CatS(-/-) chimeras. However, leukocyte CatS deficiency markedly changed plaque morphology and led to a dramatic reduction in necrotic core area by 77% and an abundance of large foam cells. Plaques of CatS(-/-) chimeras contained 17% more macrophages, 62% less SMCs, and 33% less intimal collagen. The latter two could be explained by a reduced number of elastic lamina fractures. Moreover, macrophage apoptosis was reduced by 60% with CatS deficiency. In vitro, CatS was found to be involved in cholesterol metabolism and in macrophage apoptosis in a collagen and fibronectin matrix.

CONCLUSIONS

Leukocyte CatS deficiency results in considerably altered plaque morphology, with smaller necrotic cores, reduced apoptosis, and decreased SMC content and collagen deposition and may thus be critical in plaque stability.

Delivery of cholesteryl-conjugated phosphorothioate oligodeoxynucleotides to Kupffer cells by lactosylated low-density lipoprotein

The efficacy of antisense oligonucleotides depends on the ability to reach in vivo their target cells. We aim to develop strategies to enhance uptake of phosphorothioate oligodeoxynucleotides by Kupffer cells. To this end, we conjugated cholesterol to ISIS-3082, a phosphorothioate oligodeoxynucleotide specific for intercellular adhesion molecule-1. The cholesterol-conjugated oligonucleotide, denoted ISIS-9388, associated readily with lactosylated low-density lipoprotein (LacLDL), a lipidic carrier that is taken up by galactose receptors on Kupffer cells. Association of up to 10 molecules of ISIS-9388 per LacLDL particle did not induce aggregation. LacLDL-associated [3H]ISIS-9388 was rapidly taken up by the liver after injection into rats (52.9+/-1.8% of the dose within 2 min versus 18.6+/-2.8% for ISIS-3082). N-acetylgalactosamine inhibited hepatic uptake, indicating involvement of galactose-specific receptors. Liver cells were isolated at 60 min after injection of LacLDL-associated [3H]ISIS-9388. Kupffer cells displayed the highest uptake: 88.1+/-24.7 ng of oligonucleotide/mg of cell protein, which is 6-14 times higher than after injection of free ISIS-9388 or ISIS-3082 (15.0+/-3.8 ng and 6.3+/-1.4 ng, respectively). It can be calculated that Kupffer cells contribute 43.9+/-5.4% to the liver uptake (free ISIS-9388 and ISIS-3083 14.5+/-3.1% and 8.3+/-3.2%, respectively). In conclusion, conjugation of a phosphorothioate oligodeoxynucleotide with cholesterol and its subsequent association with LacLDL results in a substantially increased Kupffer cell uptake of the oligonucleotide. As Kupffer cells play a key role in inflammation, our approach may be utilized to improve antisense-based therapeutic intervention during inflammation.

A Rett syndrome patient with a ring X chromosome: further evidence for skewing of X inactivation and heterogeneity in the aetiology of the disease

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder, characterised by regression of development in young females. Recently, mutations in the MECP2 gene were found to be present in 80% of sporadic cases, but in much lower frequency (< 30%) among familial cases. Several reports claim that the pattern of X chromosome inactivation (XCI) relates to the penetrance of RTT; in some cases skewed XCI is seen in Rett patients, and in others it is observed among normal carriers. We present here a case of RTT with a 46,X,r(X) in which complete skewed inactivation of the ring was demonstrated. Further, no mutations were found in the MECP2 gene present on the intact X. Our data, in conjunction with two previously published cases of X chromosome abnormalities in RTT, indicate that X chromosome rearrangements are sporadically associated with RTT in conjunction with extreme skewing of X inactivation. Based on our case and reported data, we discuss the evidence for a second X-linked locus for RTT associated with lower penetrance, and a different pattern of XCI, than for MECP2. This would result in a larger proportion of phenotypically normal carrier women transmitting the mutation for this putative second locus, and account for the minority of sporadic and majority of familial cases that are negative for MECP2 mutations.

Atrial fibrillation in the goat induces changes in monophasic action potential and mRNA expression of ion channels involved in repolarization

INTRODUCTION

Sustained atrial fibrillation (AF) is characterized by a marked shortening of the atrial effective refractory period (AERP) and a decrease or reversal of its physiologic adaptation to heart rate. The aim of the present study was to investigate whether the AF-induced changes in AERP in the goat are associated with changes in the atrial monophasic action potential (MAP) and whether an abnormal expression of specific ion channels underlies such changes.

METHODS AND RESULTS

Following thoracotomy, MAPs were recorded from the free wall of the right atrium both before induction of AF (control) and after cardioversion of sustained AF (>2 months) in chronically instrumented goats. In control goats, MAP duration at 80% repolarization (MAPD80) shortened (P < 0.01) from 132+/-4 msec during slow pacing (400-msec interval) to 86+/-10 msec during fast pacing (180 msec). After cardioversion of sustained AF, the MAPD80 during slow pacing was as short as 67+/-5 msec (electrical remodeling). Increasing the pacing rate resulted in prolongation (P = 0.02) of the MAPD80 to 91+/-6 msec. Also, MAPD20 (20% repolarization) shortened (P = 0.05) from 32+/-4 msec (400 msec) to 14+/-7 msec (180 msec) in the control goats, whereas it prolonged (P = 0.03) from 20+/-3 msec (400 msec) to 33+/-5 msec (180 msec) in sustained AF. mRNA expression of the L-type Ca2+ channel alpha1c gene and Kv1.5 potassium channel gene, which underlie ICa and IKur, respectively, was reduced in sustained AF compared with sinus rhythm by 32% (P = 0.01) and 45% (P < 0.01), respectively. No significant changes were found in the mRNA levels of the rapid Na+ channel, the Na+/Ca2+ exchanger, or the Kv4.2/4.3 channels responsible for Ito.

CONCLUSION

AF-induced electrical remodeling in the goat comprises shortening of MAPD and reversal of its physiologic rate adaptation. Changes in the time course of repolarization of the action potential are associated with changes in mRNA expression of the alpha subunit genes of the L-type Ca2+ channel and the Kv1.5 potassium channel.

Modulation of plasma protein binding and in vivo liver cell uptake of phosphorothioate oligodeoxynucleotides by cholesterol conjugation

Several studies have shown improved efficacy of cholesteryl-conjugated phosphorothioate antisense oligodeoxynucleotides. To gain insight into the mechanisms of the improved efficacy in vivo, we investigated the disposition of ISIS-9388, the 3'-cholesterol analog of the ICAM-1-specific phosphorothioate oligodeoxynucleotide ISIS-3082, in rats. Intravenously injected [(3)H]ISIS-9388 was cleared from the circulation with a half-life of 49.9 +/- 2.2 min (ISIS-3082, 23.3 +/- 3.8 min). At 3 h after injection, the liver contained 63.7 +/- 3. 3% of the dose. Compared to ISIS-3082, the hepatic uptake of ISIS-9388 is approximately 2-fold higher. Endothelial, Kupffer and parenchymal cells accounted for 45.7 +/- 5.7, 33.0 +/- 5.9 and 21.3 +/- 2.6% of the liver uptake of [(3)H]ISIS-9388, respectively, and intracellular concentrations of approximately 2, 75 and 50 microM, respectively, could be reached in these cells (1 mg/kg dose). Preinjection with polyinosinic acid or poly-adenylic acid reduced the hepatic uptake of [(3)H]ISIS-9388, which suggests the involvement of (multiple) scavenger receptors. Size exclusion chromatography of mixtures of the oligonucleotides and rat plasma indicated that ISIS-9388 binds to a larger extent to high molecular weight proteins than ISIS-3082. Analysis by agarose gel electrophoresis indicated that ISIS-9388 binds more tightly to plasma proteins than ISIS-3082. The different interaction of the oligonucleotides with plasma proteins possibly explains their different dispositions. We conclude that cholesterol conjugation results in high accumulation of phosphorothioate oligodeoxynucleotides in various liver cell types, which is likely to be beneficial for antisense therapy of liver-associated diseases.

Widening of the excitable gap during pharmacological cardioversion of atrial fibrillation in the goat: effects of cibenzoline, hydroquinidine, flecainide, and d-sotalol

BACKGROUND

Previous studies suggest that the antifibrillatory action of class I and III drugs is due to prolongation of the atrial wavelength. The aim of the present study was to directly evaluate the electrophysiological action of antifibrillatory drugs in a goat model of chronic atrial fibrillation (AF).

METHODS AND RESULTS

Six goats were instrumented with multiple atrial electrodes, and sustained AF was induced by electrical remodeling. During sustained AF, the effects of intravenous infusion of cibenzoline, hydroquinidine, flecainide, and d-sotalol on AF cycle length (AFCL), refractory period (RP(AF)), conduction velocity (CV(AF)), pathlength (PL(AF)), wavelength (WL(AF)), temporal (AFCL-RP(AF)), and spatial (PL(AF)-WL(AF)) excitable gap were studied. The RP(AF) was measured by determining the earliest moment at which single stimuli could capture the fibrillating atria. CV(AF) was measured during regional entrainment of AF. Contrary to our expectation, cardioversion of AF could not be attributed to prolongation of WL(AF). Hydroquinidine and d-sotalol did not affect WL(AF) significantly, whereas cibenzoline and flecainide even shortened WL(AF) by 18% and 36%, respectively. PL(AF) was increased by hydroquinidine and d-sotalol by 30%, whereas cibenzoline and flecainide did not prolong PL(AF). The only parameter that correlated consistently with cardioversion of AF was a widening of the temporal excitable gap (cibenzoline 176%, hydroquinidine 105%, flecainide 86%, d-sotalol 88%).

CONCLUSIONS

Pharmacological cardioversion of AF cannot be explained by prolongation of WL(AF). An alternative explanation for the antifibrillatory effect of class I and III drugs may be a widening of the temporal excitable gap.

Repetitive electrical remodeling by paroxysms of atrial fibrillation in the goat: no cumulative effect on inducibility or stability of atrial fibrillation

INTRODUCTION

Episodes of atrial fibrillation (AF) are known to cause both a rapid reduction in atrial refractoriness (atrial electrical remodeling) and a more delayed increase in AF stability in the chronic goat model. The aims of this study were to examine (1) the hypothesis that an AF-induced increase in AF stability might be due to a mechanism with a longer onset and offset than that of changes in refractoriness and (2) the possibility that repeated paroxysms of maintained AF might cause a cumulative increase in AF stability independent of changes in atrial refractoriness.

METHODS AND RESULTS

AF was maintained by rapid atrial pacing in seven goats for three consecutive 5-day periods, each separated from each other by 48 hours of sinus rhythm. Assessments of atrial refractory periods, conduction velocity, AF inducibility, and duration of individual episodes of AF were attempted at intervals throughout the protocol. Forty-eight hours of sinus rhythm was just sufficient for refractoriness changes to fully reverse in all goats, with no evidence of any "residual" increase in AF inducibility. There was no significant difference among any of the three periods of pacing-maintained AF with regard to time to develop episodes of AF of 60-second duration (22.1+/-13, 23.8+/-16, and 30.3+/-29 hours), 1-hour duration (56.6+/-28, 61.3+/-31, and 60.1+/-32 hours), or 24-hour duration (84.0+/-31, 87.0+/-33, and 83.5+/-32 hours).

CONCLUSION

There is no evidence for a cumulative effect of AF paroxysms on AF inducibility or stability independent of changes in refractoriness. These findings highlight the importance of atrial refractoriness as a potential target for antiarrhythmic strategies aimed at inhibiting the self-perpetuation of AF.

Pharmacologic cardioversion of chronic atrial fibrillation in the goat by class IA, IC, and III drugs: a comparison between hydroquinidine, cibenzoline, flecainide, and d-sotalol

INTRODUCTION

Recently, we reported that repetitive induction of atrial fibrillation (AF) in the goat causes electrical remodeling of the atria leading to the development of sustained AF. The aim of the present study was to compare Class IA, IC, and III drugs in their ability to cardiovert chronic AF in remodeled atria.

METHODS AND RESULTS

In 16 goats with sustained AF, hydroquinidine (HQ), cibenzoline (Ci), flecainide (FI), and d-sotalol (dS) were infused. HQ, Ci, Fl, and dS restored sinus rhythm (SR) in 83%, 91%, 67%, and 92% of the cases, while adverse drug effects occurred in 17%, 36%, 56%, and 8%. Prior to restoration of SR, AF cycle length prolonged by 68%, 103%, 53%, and 20%, respectively. The QRS width increased by 14%, 64%, and 58% (HQ, Ci, and Fl), and remained unchanged by administration of dS. RR intervals were slightly prolonged by HQ, Ci, and Fl, and markedly prolonged by dS (48%). The QT interval was moderately prolonged by HQ, Ci, and Fl, and considerably by dS (34%). QTc was only slightly prolonged by each of the drugs. Directly after cardioversion of AF, the atrial refractory period was 87+/-29 (HQ), 119+/-32 (Ci), 66+/-10 (Fl), and 73+/-18 msec (dS) (control: 146+/-18 msec). Atrial conduction velocity was 85+/-6, 71+/-11, 86+/-12, and 110+/-11 cm/sec compared with a control value of 116+/-10 cm/sec. Because directly after cardioversion the atrial wavelength was still very short (5.7 to 8.4 cm), the vulnerability for AF was still very high, and a single premature beat reinduced AF in 71% (Ci) to 100% (HQ, Fl, and dS) of the cases.

CONCLUSION

In a goat model of sustained AF, Class IA, IC, and III drugs restored sinus rhythm in 67% to 92% of the cases. However, after cardioversion, the atrial wavelength was still abnormally short, and AF was readily inducible in 71% to 100% of the cases.

Mechanisms of pharmacologic cardioversion of atrial fibrillation by Class I drugs

INTRODUCTION

We recently developed a goat model of sustained atrial fibrillation (AF) in which repetitive induction of AF by burst pacing shortened the atrial effective refractory period (AERP) (electrophysiologic remodeling) and progressively prolonged the paroxysms of AF to become sustained (24 hours) within 1 to 3 weeks (atrial fibrillation begets atrial fibrillation). The aim of the present study was to study the effect of Class I drugs in this animal model of chronic AF.

METHODS AND RESULTS

The effects of hydroquinidine (HQ) on seven chronically fibrillating goats and of flecainide (Fl) on nine goats were studied. Both drugs were infused intravenously until sustained AF was cardioverted or adverse drug effects occurred. HQ and Fl restored sinus rhythm in 86% and 67% of the cases. Adverse drug effects occurred in 14% and 56%, respectively. The average atrial cycle length of AF (AFCL) was prolonged to a different degree. Just before restoration of sinus rhythm, the two drugs had increased AFCL by 72% and 50%. The duration of the QRS complex was prolonged 17% by HQ and 50% by Fl. The RR interval was not affected by HQ and was prolonged slightly by Fl. Directly after restoration of sinus rhythm, the AERP during pacing with an interval of 400 msec was 92 +/- 29 (HQ) and 66 +/- 10 msec (Fl) (control value: 149 +/- 10 msec). Intra-atrial conduction velocity was 83 +/- 7 and 86 +/- 11 cm/sec (control value: 116 +/- 10 cm/sec). Although both drugs were effective in terminating AF, after cardioversion the atrial vulnerability was still very high and a single premature stimulus reinduced AF in 100% of the animals. As a result of the short AERP by the AF-induced remodeling and the depressed intra-atrial conduction by the Class I drugs, directly after cardioversion the atrial wavelength was abnormally short (between 5.7 and 7.5 cm). This explains the still high atrial vulnerability to AF directly after cardioversion by Class I drugs. Surprisingly, the prolongation of AFCL by either Class I drug was not due to lengthening of the functional refractory period but rather to a widening of the excitable gap during AF.

CONCLUSION

In a goat model of chronic AF, infusion of Class IA and Class IC drugs restored sinus rhythm in 67% to 86% of the cases. However, due to the short AERP and the depressed intra-atrial conduction directly after cardioversion, the atrial vulnerability was still very high and a premature beat easily reinduced AF.

Electrical remodeling due to atrial fibrillation in chronically instrumented conscious goats: roles of neurohumoral changes, ischemia, atrial stretch, and high rate of electrical activation

BACKGROUND

Recently, we developed a goat model of chronic atrial fibrillation (AF). Due to AF, the atrial effective refractory period (AERP) shortened and its physiological rate adaptation inversed, whereas the rate and stability of AF increased. The goal of the present study was to evaluate the role of (1) the autonomic nervous system, (2) ischemia, (3) stretch, (4) atrial natriuretic factor (ANF), and (5) rapid atrial pacing in this process of electrical remodeling.

METHODS AND RESULTS

Twenty-five goats were chronically instrumented with multiple epicardial atrial electrodes. Infusion of atropine (1.0 mg/kg; n=6) or propranolol (0.6 mg/kg; n=6) did not abolish the AF-induced shortening of AERP or interval (AFI). Blockade of K+(ATP) channels by glibenclamide (10 micromol/kg; n=6) slightly increased the AFI from 95+/-4 to 101+/-5 ms, but AFI remained considerably shorter than during acute AF (145 ms). Glibenclamide had no significant effect on AERP after electrical cardioversion of AF (69+/-14 versus 75+/-15 ms). Volume loading by 0.5 to 1.0 L of Hemaccel (n=12) did not shorten AERP. The median plasma level of ANF increased from 42 to 99 pg/mL after 1 to 4 weeks of AF (n=6), but ANF infusion (0.1 to 3.1 microg/min, n=4) did not shorten AERP. Rapid atrial pacing (24 to 48 hours; n=10) progressively shortened AERP from 134+/-10 to 105+/-6 ms and inversed its physiological rate adaptation.

CONCLUSIONS

Electrical remodeling by AF is not mediated by changes in autonomic tone, ischemia, stretch, or ANF. The high rate of electrical activation itself provides the stimulus for the AF-induced changes in AERP.

Atrial fibrillation begets atrial fibrillation. A study in awake chronically instrumented goats

BACKGROUND

In this study we tested the hypothesis that atrial fibrillation (AF) causes electrophysiological changes of the atrial myocardium which might explain the progressive nature of the arrhythmia.

METHODS AND RESULTS

Twelve goats were chronically instrumented with multiple electrodes sutured to the epicardium of both atria. Two to 3 Weeks after implantation, the animals were connected to a fibrillation pacemaker which artificially maintained AF. Whereas during control episodes of AF were short lasting (6 +/- 3 seconds), artificial maintenance of AF resulted in a progressive increase in the duration of AF to become sustained (> 24 hours) after 7.1 +/- 4.8 days (10 of 11 goats). During the first 24 hours of AF the median fibrillation interval shortened from 145 +/- 18 to 108 +/- 8 ms and the inducibility of AF by a single premature stimulus increased from 24% to 76%. The atrial effective refractory period (AERP) shortened from 146 +/- 19 to 95 +/- 20 ms (-35%) (S1S1, 400 ms). At high pacing rates the shortening was less (-12%), pointing to a reversion of the normal adaptation of the AERP to heart rate. In 5 goats, after 2 to 4 weeks of AF, sinus rhythm was restored and all electrophysiological changes were found to be reversible within 1 week.

CONCLUSIONS

Artificial maintenance of AF leads to a marked shortening of AERP, a reversion of its physiological rate adaptation, and an increase in rate, inducibility and stability of AF. All these changes were completely reversible within 1 week of sinus rhythm.