An overview of the safety pharmacology career of Dr. C.R. Hassler.

Each year the Safety Pharmacology Society (SPS) recognizes an investigator who has had a marked impact upon the discipline. The 2016 recipient of the SPS Distinguished Service Award (DSA) was Dr. Craig R. Hassler. Dr. Hassler is one of the founding members of the SPS and has been actively engaged in physiological research for over 46years. Dr. Hassler delivered a talk entitled "My 43Years at Battelle Memorial Institute" to meeting attendees. In this article an overview is provided of the illustrious career of Dr. Hassler along with an account of the numerous animal models that were developed at Battelle under his guidance over the years.

The safety of high-dose buprenorphine administered subcutaneously in cats.

The safety of a proprietary formulation of buprenorphine hydrochloride administered subcutaneously (SC) to young cats was investigated in a blinded, randomized study. Four cohorts of eight cats aged approximately 4 months were administered saline, 0.24, 0.72 or 1.20 mg/kg/day buprenorphine SC for nine consecutive days, representing 0×, 1×, 3× and 5× of the intended dose. Cats were monitored daily for evidence of clinical reactions, food and water intake and adverse events (AEs). Physical examinations, clinical pathology, vital signs and electrocardiograms (ECGs) were evaluated at protocol-specified time points. Complete necropsy and histopathologic examinations were performed following humane euthanasia. Four buprenorphine-treated cats experienced AEs during the study, two unrelated and two related to study drug administration. The two cats with AEs considered related to drug administration had clinical signs of hyperactivity, difficulty in handling, disorientation, agitation and dilated pupils in one 0.24 mg/kg/day cat and one 0.72 mg/kg/day cat. All of these clinical signs were observed simultaneously. There were no drug-related effects on survival, injection response, injection site inspections, body weight, food or water consumption, bleeding time, urinalysis, respiration rate, heart rate, ECGs, blood pressures, body temperatures, macroscopic examinations or organ weights. Once daily buprenorphine s.c. injections at doses of 0.24, 0.72 and 1.20 mg/kg/day for 9 consecutive days were well tolerated in young domestic cats.

n-3 (omega-3) polyunsaturated fatty acids prevent acute atrial electrophysiological remodeling.

BACKGROUND AND PURPOSE: Recent reports suggest that n-3 (omega-3) polyunsaturated fatty acids (PUFAs) may reduce atrial fibrillation (AF). Reduction of the atrial effective refractory period (ERP) is believed to be an important early remodeling event that favors the development and perpetuation of AF. We hypothesized that n-3 PUFAs would attenuate early atrial electrophysiolgical remodeling in a canine model of acute atrial tachypacing. EXPERIMENTAL APPROACH: Adult dogs of either sex received n-3 PUFAs (n=6), n-6 PUFAs (n=6), or saline (n=6) infused over 1 h. After a stable ERP was established, treatment was initiated concurrently with 6 h of rapid atrial pacing (400 b.p.m.). Serial right atrial ERPs were measured during rapid atrial pacing, and induction of atrial tachyarrhythmias was attempted at the conclusion of each study. KEY RESULTS: There was no change in P wave duration or in the PQ, QRS, QT or QTc intervals in any of the treatment groups. N-3 PUFA treatment significantly reduced the shortening of atrial ERP, compared to both control groups (P<0.05). In separate experiments, the same n-3 PUFA infusion was given to dogs remaining in normal sinus rhythm. During sinus rhythm, n-3 PUFA infusion did not alter any electrocardiogram (ECG) parameter or the atrial ERP. CONCLUSIONS AND IMPLICATIONS: We conclude that acute n-3 PUFA treatment prevents acute atrial electrophysiological remodeling during high rate activity, which may minimize the self-perpetuation of AF.

Assessment of drug-induced QT interval prolongation in conscious rabbits.

INTRODUCTION: Most preclinical trials are designed to identify potential torsadogenicity test only for surrogates of torsade de pointes, most commonly prolongation of the heart rate corrected QT interval (QTc). This study was conducted to determine which correction method best accounts for the effects of changes in the RR interval on the QT interval of conscious rabbits. This study was also conducted to validate the use of conscious, sling-trained rabbits to assess the QTc interval, and to evaluate the reliability and accuracy of this preparation in predicting drug-induced QTc prolongation in humans. METHODS: ECGs were recorded via bipolar transthoracic ECG leads in 7 conscious rabbits previously trained to rest quietly in slings. The heart rate was slowed with 2.0 mg/kg zatebradine to assess the effects of heart rate on the QT interval. The same ECG and sling preparation was used to evaluate the effects in of three drugs known to be torsadogenic in humans (cisapride, dofetilide and haloperidol), two drugs known to be non-torsadogenic in humans (propranolol and enalaprilat) and a control article (vehicle). All of the test articles were administered intravenously to 4 rabbits, and both RR and QT intervals were measured and the corrected QT values were calculated by an investigator blinded to the test article, utilizing our own algorithm (QTc=QT/(RR)(0.72)) which permitted the least dependency of QTc on RR interval. RESULTS: The following regression equations were obtained relating QT to RR: QT=2.4RR(0.72), r(2)=0.79, with RR intervals varying between 210 and 350 ms. QTc lengthened significantly in all conscious rabbits given intravenous cisapride, dofetilide and haloperidol (p<0.05), and QTc did not change with DMSO (vehicle control), propranolol or enalaprilat. DISCUSSION: Results indicate that a bipolar transthoracic ECG recorded in conscious, sling-trained rabbits may provide an easy and economical methodology useful in predicting QTc lengthening of novel pharmacological entities.

Ascorbate attenuates atrial pacing-induced peroxynitrite formation and electrical remodeling and decreases the incidence of postoperative atrial fibrillation.

Atrial fibrillation (AF), the most common chronic arrhythmia, increases the risk of stroke and is an independent predictor of mortality. Available pharmacological treatments have limited efficacy. Once initiated, AF tends to self-perpetuate, owing in part to electrophysiological remodeling in the atria; however, the fundamental mechanisms underlying this process are still unclear. We have recently demonstrated that chronic human AF is associated with increased atrial oxidative stress and peroxynitrite formation; we have now tested the hypothesis that these events participate in both pacing-induced atrial electrophysiological remodeling and in the occurrence of AF following cardiac surgery. In chronically instrumented dogs, we found that rapid (400 min(-1)) atrial pacing was associated with attenuation of the atrial effective refractory period (ERP). Treatment with ascorbate, an antioxidant and peroxynitrite decomposition catalyst, did not directly modify the ERP, but attenuated the pacing-induced atrial ERP shortening following 24 to 48 hours of pacing. Biochemical studies revealed that pacing was associated with decreased tissue ascorbate levels and increased protein nitration (a biomarker of peroxynitrite formation). Oral ascorbate supplementation attenuated both of these changes. To evaluate the clinical significance of these observations, supplemental ascorbate was given to 43 patients before, and for 5 days following, cardiac bypass graft surgery. Patients receiving ascorbate had a 16.3% incidence of postoperative AF, compared with 34.9% in control subjects. In combination, these studies suggest that oxidative stress underlies early atrial electrophysiological remodeling and offer novel insight into the etiology and potential treatment of an enigmatic and difficult to control arrhythmia. The full text of this article is available at http://www.circresaha.org.

Sodium pentobarbital versus alpha-chloralose anesthesia. Experimental production of substantially different slopes in the transmural CP/ATP ratios within the left ventricle of the canine myocardium.

BACKGROUND: Transmural analyses of the creatine phosphate (CP)/ATP ratio in various lamina of the canine myocardium have previously revealed significant variations in the CP/ATP ratio, with the subendocardial layer displaying a decreased ratio relative to the subepicardial layer. Without exception, these results were obtained under sodium pentobarbital anesthesia. These findings have been interpreted to imply that the normal endocardium may be operating in the oxygen-limited domain or that there are transmurally varying set points for the regulation of oxidative phosphorylation. METHODS AND RESULTS: In this work, we examine the effect of the anesthetic regimen on the transmural CP/ATP ratio within the left ventricular wall of the canine myocardium using spatially localized 31P-nuclear magnetic resonance (NMR) and an open-chest model. Two anesthetics were compared, alpha-chloralose and sodium pentobarbital. Under sodium pentobarbital, the CP/ATP ratio ranged from 1.92 +/- 0.06 to 2.51 +/- 0.08 from endocardium to epicardium, resulting in a transmural slope in the CP/ATP ratio of 0.149 +/- 0.047 (n = 22). Under alpha-chloralose, CP/ATP ratios ranged from 2.18 +/- 0.05 to 2.32 +/- 0.06, with a transmural slope of 0.035 +/- 0.018 (n = 38). Thus, the transmural slope in CP/ATP ratio was nearly four times greater with sodium pentobarbital than with alpha-chloralose, and the difference in these slopes was statistically significant (P = .029). No difference was observed in average CP/ATP obtained from the entire wall with either anesthetic. CONCLUSIONS: These results demonstrate that the transmural trend in CP/ATP ratio previously reported in the myocardium is likely to be a direct reflection of the sodium pentobarbital anesthetic regimen, not truly reflecting the trend in the normal unanesthetized animal. Moreover, since the transmural variation in CP/ATP ratio was greatly reduced with alpha-chloralose, it appears unlikely that the endocardium in the normal unanesthetized heart is operating in the oxygen-limited domain. These results also point to the importance of the anesthetic regimen in biochemical analysis, indicate the necessity of increased caution in directly translating results obtained under anesthesia, and demonstrate the unique power of in vivo NMR to extract such subtle biochemical information.

Transmural saturation transfer analysis of the creatine kinase system in the mammalian heart.

31P NMR spatial localization and saturation transfer techniques were combined to enable the transmural measurement of the forward creatine kinase (CK) rate (ATP:creatine N-phosphotransferase, EC 2.7.3.2.) in the in vivo canine myocardium. Five epicardial towards endocardial regions of the left ventricle (LV) were simultaneously examined using spatially localized voxels. Although intraleft ventricular CP/ATP ratios were constant, the pseudo first order rate constant (k') and the forward creatine kinase rate (Rf) displayed a 61% variation across the LV wall. Because CK levels and calculated [ADP], [CP] and pH are transmurally invariant in the normal left ventricle, the observed changes in the Rf could not be explained by changes in the absolute levels of these substrates and of creatine kinase. In addition, because myocardial oxygen consumption rates are known to be higher in the endocardium, these results imply that forward creatine kinase rates are not directly related to oxidative phosphorylation rates.

Usefulness of a free radical scavenger in preventing doxorubicin-induced heart failure in dogs.

This study was designed to investigate whether either of 2 dosage schedules of N-acetylcysteine (NAC) was effective in preventing chronic doxorubicin-induced heart failure in dogs. Thirty-eight dogs were randomly assigned to 1 of 4 groups: controls, 10 dogs; doxorubicin only, 12 dogs; doxorubicin + low dose NAC, 8 dogs; and doxorubicin + high dose NAC, 8 dogs. All dogs except the controls received 1 mg/kg of doxorubicin weekly for 8 weeks and then every other week for 8 weeks. The doxorubicin + low-dose NAC group received 140 mg/kg of NAC 30 minutes before each dose of doxorubicin. The doxorubicin + high-dose NAC group received NAC before and then twice a day for 5 days. Systolic time intervals and echocardiograms were obtained weekly; cardiac catheterization was performed at the conclusion of the study. Of the 38 dogs in the study, 9 died; all deaths were in the doxorubicin treatment groups. The incidence of death was not different between the doxorubicin-only, the doxorubicin + low-dose and the doxorubicin + high-dose NAC groups. The noninvasive and the invasive and the catheterization data generally revealed poorer cardiac function of the doxorubicin treatment groups than in controls. However, no significant differences existed between the doxorubicin-only and doxorubicin + low-dose and doxorubicin + high-dose NAC groups. In conclusion, NAC in a low- or high-dose regimen did not significantly ameliorate doxorubicin cardiac toxicity. Because NAC is a free radical scavenger, perhaps doxorubicin cardiac toxicity is not a result of free radical generation.