• Open Access

Short-Term Effects of Atorvastatin in Normal Dogs and Dogs with Congestive Heart Failure Due to Myxomatous Mitral Valve Disease

Authors


  • Partial results of this study were presented as an abstract at the 2008 ACVIM Forum in San Antonio, TX.

Corresponding author: S.M. Cunningham, Department of Clinical Sciences, Tufts Cummings School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA 01536; e-mail: suzanne.cunningham@tufts.edu.

Abstract

Background

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) may improve heart failure class and survival in people with congestive heart failure (CHF) of various etiologies.

Hypothesis/Objectives

To evaluate the tolerability of atorvastatin in healthy dogs, and the short-term effects of atorvastatin on clinical markers of disease severity, lipid profiles, and markers of systemic inflammation and oxidative stress in dogs with CHF.

Animals

Eleven normal dogs and 12 client-owned animals with CHF attributable to myxomatous mitral valve disease.

Methods

Prospective nonblinded observational study. Normal dogs (n = 11) were first treated with atorvastatin and re-evaluated after 14 and 30 days for clinical tolerability and alterations in certain laboratory results. Subsequently, dogs with CHF (n = 12) were treated with atorvastatin at a dosage of 2 mg/kg q24h for 8 weeks. Echocardiography, blood pressure (BP), quality of life questionnaire, and blood sampling were performed pre and post atorvastatin administration.

Results

Atorvastatin was well tolerated and did not result in apparent adverse effects or biochemical abnormalities in healthy dogs and in dogs with CHF. Healthy dogs experienced a decrease in total cholesterol (TC) concentration (= .03) after atorvastatin administration. Decreases in TC concentration (= .02), non-HDL cholesterol concentration (= .02), total white blood cell count (= .03), neutrophils (= .01), and systolic BP (= .01) were noted in the CHF group after 8 weeks of atorvastatin.

Conclusions and Clinical Importance

Atorvastatin was well tolerated at clinically relevant doses in healthy dogs and dogs with CHF. Further investigation into the effects of statin treatment in dogs with CHF is warranted.

Abbreviations
BP

blood pressure

CBC

complete blood count

CHF

congestive heart failure

CK

creatine kinase

CRP

C-reactive protein

CV

coefficient of variation

ELISA

enzyme-linked immunosorbent assay

FS

fractional shortening

HDL-C

high-density lipoprotein

HR

heart rate

ISACHC

International Small Animal Cardiac Health Council

La:Ao

left atrial to aortic root ratio

LDL

low-density lipoprotein

MMVD

myxomatous mitral valve disease

MR

mitral regurgitation

NT-proBNP

N-terminal pro-B-type natriuretic peptide

RPS

right parasternal

TC

total cholesterol

VHS

vertebral heart score

WBC

white blood cells

There is evidence from human clinical trials that treatment with statin drugs (3-hydroxy-3-methylglutaryl coenzyme A [HMG-CoA] reductase inhibitors) may improve outcomes associated with both ischemic and nonischemic heart disease.[1-3] Although these drugs are best known for their cholesterol-lowering properties, emerging evidence suggests that the benefits of statin treatment extend beyond their lipid-lowering effects.[1, 4] Beneficial pleiotropic (noncholesterol-dependent) effects of statins include antioxidant and antithrombotic properties, potent inhibition of inflammatory responses, antiarrhythmic effects, improved endothelial function, and inhibition of myocardial hypertrophy.[4] In people with nonischemic systolic heart failure, statin treatment may attenuate left ventricular dilatation and improve cardiac function and exercise tolerance.[3] Statins also have been shown to have survival benefits in some but not all studies of people with various etiologies of heart failure.[2, 3] The results of 1 large meta-analysis of statin heart failure trials suggested that lipophilic statins (eg, atorvastatin, simvastatin) may confer a mortality benefit not seen in those patients randomized to hydrophilic statin drugs (eg, rosuvastatin).[2]

The lipophilic HMG-CoA reductase inhibitor atorvastatin is the most commonly prescribed statin drug in humans. The drug generally is very well tolerated in people, with uncommon adverse effects including mild gastrointestinal upset, skeletal myopathy, and increased hepatic transaminase activity. Similar dose-related adverse effects have been seen in dogs given atorvastatin experimentally at dosages exceeding 40 mg/kg.[5] Although high-dose toxicity studies have been performed in research dogs,[5] the tolerability and short-term effects of atorvastatin at clinically relevant dosages have not previously been assessed in normal dogs or dogs with spontaneous cardiac disease.

Statin drugs exert diverse cardioprotective and systemic anti-inflammatory effects that have salutary effects in people with congestive heart failure (CHF) and may hold promise as novel therapeutic agents for treatment of CHF in dogs. The goals of this exploratory study were 2-fold: (1) to evaluate the tolerability and cholesterol-decreasing properties of 2 dosages of the HMG-CoA reductase inhibitor, atorvastatin, in healthy dogs; and (2) to assess the short-term effects of atorvastatin on clinical markers of disease severity and circulating markers of systemic inflammation and oxidative stress in dogs with CHF.

Materials and Methods

Employee-owned healthy dogs were enrolled on the basis of normal history, physical examination findings, complete blood count (CBC),1 serum biochemistry profile1 and echocardiography (Sonos 4500 system).2 Atorvastatin3 was administered by the dogs' owners at a dosage of 0.5 mg/kg q24h for 2 weeks, and the dosage was increased to 2 mg/kg q24h for the next 2 weeks. CBCs, biochemistry profiles, and C-reactive protein (CRP)4 concentrations were evaluated after an 8-hour fast at baseline and repeated after 2 and 4 weeks of atorvastatin administration.

After confirmation of tolerance of atorvastatin in healthy dogs, client-owned dogs with stable International Small Animal Cardiac Health Council (ISACHC)[6] Class II or IIIa CHF secondary to myxomatous mitral valve disease (MMVD) or dilated cardiomyopathy (DCM) were enrolled. All dogs with CHF had previous radiographic and clinical evidence of CHF that responded to appropriate medical management. At the time of study enrollment, dogs were required to have good clinical control of CHF and to have been on a stable medical management regimen for ≥7 days. Dogs with other clinically relevant comorbid conditions, including current or historical hepatic disease or myopathy, infection or neoplasia, chronic kidney disease, or poorly controlled endocrinopathy were excluded from the study.

Echocardiography (ECG), including standard M-mode, 2-dimensional (2D), color-flow, and spectral Doppler were performed by a single unblinded examiner (SMC). All examinations were performed in unsedated dogs positioned in right lateral recumbency. Standard M-mode dimensions were obtained in right parasternal (RPS) short axis views using 2D guidance and measured using the leading edge-to-leading edge method.[7] The 2-dimensional left atrial size (2D-LA) was obtained in the RPS short axis view in the first frame after aortic valve closure. Continuous ECG monitoring was implemented during the echocardiographic examination. All dogs were fasted for ≥8 hours before each blood collection. Dogs with CHF were given atorvastatin (2 mg/kg q24h) by their owners for 8 weeks. CBCs and biochemistry profiles were obtained at baseline and repeated after 2 and 8 weeks of atorvastatin administration. The echocardiogram, ECG (Pagewriter 200),2 BP measurement,5 owner-completed functional evaluation of cardiac health (FETCH) questionnaire,[8] cholesterol fractionation,6 CRP, N-terminal pro-B-type natriuretic peptide (NT-proBNP),7 and plasma 8-F-isoprostane concentrations8 were all measured at baseline and re-evaluated after 8 weeks. The main echocardiographic parameters of interest were the 2D-LA,[9] fractional shortening, and normalized left ventricular end-diastolic dimension.[10] The ECG was evaluated for any clinically relevant changes in heart rate, rhythm, or QRS morphology; and, systolic blood pressure was quantified using the Doppler method. The FETCH questionnaire was analyzed as previously described.[8]

Blood was collected in EDTA tubes for measurement of CRP in all dogs. In dogs with CHF, additional blood was collected into EDTA tubes for measurement of 8-F-isoprostanes, cholesterol fractionation, and NT-proBNP. Plasma was separated by centrifugation within 30 minutes of collection and stored at −80°C until batched analysis. Before freezing, butyl-hydroxytoluene was added to the aliquot of plasma to be used for 8-F-isoprostane measurement to avoid exogenous oxidation. Plasma for NT-proBNP was shipped to the assay laboratory on ice according to guidelines established by the manufacturer and was analyzed using a commercially available assay for measurement of canine NT-proBNP. CRP concentrations were analyzed in duplicate by means of a commercially available canine-specific enzyme-linked immunosorbent assay according to the manufacturer's instructions. Plasma 8-F-isoprostane concentrations were examined by GC/MS. Plasma total cholesterol (TC), triglyceride, and high density lipoprotein (HDL) concentrations were analyzed by automated methods using enzymatic or immunoturbidometric reagents, and non-HDL (low-density lipoprotein; LDL) concentration was calculated as the difference between TC and HDL.

The study was approved by the Tufts University Institutional Animal Care and Use Committee. All owners provided written informed consent before study enrollment.

Statistical Analysis

Data were graphically inspected, and normality was assessed using the Kolmogorov–Smirnov test. Data that were normally distributed are presented as mean ± SD whereas nonparametric data are presented as median (range). All nonparametric data were logarithmically transformed before analysis. For continuous data, pre- and posttreatment variables were compared with paired t-tests. P < .05 was considered statistically significant. Data analysis was performed with commercial statistical software.9

Results

Between June 2006 and December 2007, 11 healthy dogs and 13 dogs with CHF were enrolled in the study. The healthy dogs included 7 female dogs and 4 male dogs (all neutered) of various breeds, with a mean age of 5.5 ± 2.4 years, and a mean body weight of 24.1 ± 7.8 kg. Both dosages of atorvastatin were well tolerated in the healthy dogs and no reported adverse effects or biochemical abnormalities were noted. A significant decrease in total serum cholesterol concentration compared to baseline was seen after atorvastatin administration at 2 mg/kg q24h (218 ± 34 mg/dL versus 254 ± 62 mg/dL; = .04) but not at 0.5 mg/kg q24h (236 ± 35 mg/dL versus 254 ± 62 mg/dL; = .22). No changes were noted in alanine aminotransferase activity (ALT; = .40), creatine kinase activity (CK; = .47), total leukocyte count (white blood cells [WBC]; = .13), or CRP concentration (= .73; Table 1).

Table 1. Selected variables in 11 healthy dogs at baseline and after 2 weeks of atorvastatin administration at 0.5 mg/kg q24h and 2 mg/kg q24h, respectively
 Baseline0.5 mg/kg2 mg/kg
  1. ALT, alanine aminotransferase; CK, creatine kinase; CRP, C-reactive protein; TC, total cholesterol; WBC, white blood cells.

  2. Data are presented as mean and standard deviation or median and range, as appropriate.

  3. a

     .05 compared to baseline value.

TC (mg/dL)254.4 ± 62.4236.6 ± 34.9217.9 ± 34.4a
Total WBC (cells/μL)8,400 ± 2,3207,877 ± 2,0547,700 ± 1,970
Neutrophils (cells/μL)5,590 ± 2,1435,545 ± 2,1874,945 ± 1,978
Monocytes (cells/μL)358 ± 239291 ± 178357 ± 239
CRP (μg/mL)1.08 (0.64–28.70)0.93 (0.60–20.40)1.27 (0.55–12.67)
ALT (U/L)50 ± 1557 ± 2855 ± 26
CK (U/L)120 ± 65104 ± 41136 ± 41

Thirteen dogs with ISACHC Class II CHF attributable to MMVD (n = 12) or DCM (n = 1) were enrolled in the study and all dogs finished the 8 week open trial. As only 1 dog presented with primary DCM, this animal was excluded from further analysis. There were 4 spayed females and 8 neutered males with a mean age of 10.3 ± 2.6 years and a mean body weight of 11.1 ± 11.7 kg. Dogs with CHF were older (< .001) and larger (= .005) compared to the healthy dogs at baseline. Breeds represented in the CHF group included Cavalier King Charles Spaniel (n = 2), Dachshund (n = 2), Shih Tzu (n = 2), mixed breed (n = 2), and 1 each of the following: Yorkshire Terrier, Border Collie, Cock-a-Poo, Coton de Tulear, and Bichon Frise. Background treatments were not standardized, but all dogs were treated with furosemide, an ACE inhibitor, and pimobendan. Other drugs administered in varying combinations were as follows: digoxin (n = 3), diltiazem (n = 1), spironolactone (n = 2), hydrochlorothiazide (n = 2), mexiletine (n = 1), hydrocodone (n = 1), and soloxine (n = 1). The furosemide dosage was adjusted on an as-needed basis during the study period but no other changes in diet or cardiac drugs were made during the trial. Atorvastatin appeared to be well tolerated in all dogs, with no owner-reported adverse effects. At baseline, dogs with CHF had higher total WBC (11,267 ± 2,863/μL versus 8,400 ± 2,320/μL; = .02) and neutrophil counts (8,428 ± 2,676/μL versus 5,590 ± 2,143/μL; = .01) relative to normal dogs. Dogs with CHF had significant decreases in total WBC (= .03) and segmented neutrophil (= .01) counts compared to baseline after 8 weeks of atorvastatin administration (Table 2). Decreases in TC (= .02) and LDL (= .02; Table 2) concentrations, as well as a decrease in systolic BP (= .01) were noted after 8 weeks of statin treatment (Table 2). No changes in any other measured echocardiographic, electrocardiographic, or hematologic variables were seen after atorvastatin administration to dogs with CHF (Table 2).

Table 2. Selected variables measured at baseline and after 8 weeks of atorvastatin administration (2 mg/kg q24h) in 12 dogs with congestive heart failure attributable to myxomatous mitral valve disease
 Baseline ValuePost-Atorvastatin
  1. 2D-LA, two-dimensional left atrial dimension in end-systole; ALT, alanine aminotransferase; BP, blood pressure; CK, creatine kinase; CRP, C-reactive protein; FETCH, functional evaluation of cardiac health questionnaire; FS, fractional shortening; HDL, high-density lipoprotein; LDL, low-density lipoprotein; LVEDDN, left ventricular end-diastolic dimension normalized to body size; NT-proBNP, N-terminal pro-B-type natriuretic peptide; TC, total cholesterol; WBC, white blood cells.

  2. Data are presented as mean and standard deviation or median and range, as appropriate.

  3. a

     .05 compared to baseline value.

TC (mg/dL)209.3 ± 53.4186.1 ± 41.1a
HDL (mg/dL)187.7 ± 39.9174.4 ± 34.7
LDL (mg/dL)21.6 ± 17.111.7 ± 8.6a
Total WBC (cells/μL)11,267 ± 2,8629,542 ± 2,648a
Neutrophils (cells/μL)8,428 ± 2,6766,760 ± 2,404a
Monocytes (cells/μL)520 ± 246518 ± 324
CRP (μg/mL)1.53 (0.81–4.09)1.71 (0.81–9.45)
8-F-isoprostane (pg/mL)50.1 ± 15.749.9 ± 14.6
ALT (U/L)40.1 ± 13.645.8 ± 23.0
CK (U/L)184.1 ± 134.9112.0 ± 40.3
FETCH score18.3 ± 11.516.2 ± 12.0
NT-proBNP (ng/mL; n = 9)2,017 ± 7602,106 ± 1,272
Systolic BP (mmHg)150 ± 25131 ± 30a
2D-LA (cm)4.04 ± 0.834.20 ± 1.07
FS (%)49 ± 1149 ± 11
LVEDDN (cm/kg)2.11 ± 0.272.16 ± 0.32

Discussion

In this study, clinically relevant dosages of atorvastatin were well tolerated in healthy dogs and dogs with naturally acquired CHF, with no adverse effects and no hematologic abnormalities noted. A dose-dependent decrease in TC concentration in healthy dogs was seen after 2 weeks at 2 mg/kg q24h, but not 0.5 mg/kg q24h. Dogs with CHF also exhibited decreased concentrations of TC and LDL after 8 weeks of atorvastatin at the 2 mg/kg dosage. This is consistent with previous canine toxicity studies that demonstrated dose-dependent serum cholesterol decreases in experimental dogs.[5] Although many of the beneficial cardiovascular effects of statins occur by mechanisms independent of decreases in cholesterol concentration, decreased serum cholesterol concentration may serve as a surrogate indicator of dosage efficacy. The results of this study, therefore, suggest that 2 mg/kg may be an appropriate starting dosage in dogs. By inhibiting an early step in the cholesterol biosynthetic pathway, statins also inhibit other downstream products of mevalonate metabolism, including the isoprenoid intermediates responsible for the posttranslational prenylation and activation of the Rho and Rac family of small GTPases.[4, 11] These signaling proteins negatively regulate endothelial nitric oxide synthase, and contribute to NAD(P)H-oxidase activation, angiotensin II-mediated superoxide production, and NF-κβ-induced release of pro-inflammatory mediators.[11] Inhibition of these isoprenoid-dependent signaling pathways is thought to explain many of the pleiotropic effects of statins on the cardiovascular system, including anti-inflammatory and antioxidant properties, decreased platelet inhibition, antiarrhythmic actions, and increased mobilization of endothelial progenitor cells.[4]

The aforementioned pleiotropic effects of statins are thought to contribute to improvements in ventricular function, exercise tolerance, and survival seen in some, but not all studies of people with heart failure.[1-3] There is conflicting data regarding the mortality benefit of statin drugs in this setting, raising the importance of considering differences in study design.[1, 2] It has recently been suggested that the observed discrepancies in results among various CHF trials may relate in part to differences in the type of statin used.[1, 2] A meta-analysis of randomized controlled trials of statins in people with CHF showed that randomization to lipophilic statins (eg, atorvastatin, simvastatin) conferred a significant mortality benefit not seen in those patients randomized to hydrophilic statin drugs (eg, rosuvastatin).[2] In this small study, we did not observe any significant short-term effects on echocardiographic or ECG parameters, quality of life questionnaire, or NT-proBNP. The lack of observed improvement in these clinical parameters may indicate that statins are not helpful in dogs with nonischemic heart failure, but the lack of observed effect also could relate to the small number of dogs, short duration of this trial or both. The modest decreases in systolic blood pressure seen in dogs with CHF after atorvastatin administration may have resulted from statin treatment, habituation to the hospital environment, or the effects of concomitant cardiac medications. Currently there is no clear consensus on the use of statins in people with CHF and it is clear that more trials are needed in both people and veterinary patients to better ascertain the effects of statins in the heart failure setting.

There is a growing body of evidence in both human and veterinary medicine to suggest that systemic inflammation plays an important role in the etiopathogenesis of CHF.[3, 12, 13] Although numerous inflammatory biomarkers are available, the WBC count on a standard CBC is the most readily available nonspecific marker of systemic inflammation. This study documented a relative increase in total WBC and neutrophil counts in dogs with CHF relative to healthy dogs, similar to the findings of Farabaugh et al.[14] There is considerable emerging evidence that increased WBC count is associated with adverse cardiovascular outcomes in people.[12] Increased WBC count, and in particular an increased neutrophil count, is associated with an increased risk of developing heart failure in healthy men.[12] In this analysis, significant decreases in total WBC and neutrophil counts were seen in the CHF group after both 2 and 8 weeks of atorvastatin administration. This effect was seen only in the CHF group, and the WBC count of CHF dogs no longer differed from those of the healthy dogs after statin administration. Post-atorvastatin WBC counts remained within the reference range in all animals and neutropenia was not documented. It is not clear whether the observed decrease in WBC count seen in CHF dogs was the direct result of atorvastatin, or perhaps secondary to overall better control of CHF or habituation to the hospital environment.

Statins have been shown to decrease CRP concentrations in people with cardiovascular disease,[3, 4, 15] and human patients with increased WBC and higher CRP concentrations may derive more benefit from statin administration than those without evidence of systemic inflammation.[15] No change in CRP concentration was documented after atorvastatin treatment in the dogs of this study. This is not surprising given that CRP concentrations were not increased at baseline in this small population of healthy dogs and dogs with well-controlled CHF. The authors have previously documented increased CRP concentrations in dogs with MMVD and CHF.[13] The discrepant CRP findings may be attributed to the smaller number of dogs in this study or may reflect a difference in study populations, as the previous study included dogs with more advanced ISACHC Class III CHF, whereas this study was restricted to dogs with well-controlled ISACHC Class II CHF.

There are several limitations to this study, including small sample size, lack of observer blinding, lack of pharmokinetic measurements, and most notably the lack of a placebo group. This study was intended to be exploratory in nature and larger blinded, placebo-controlled studies are needed to confirm and further characterize these findings. Nonetheless, the pleiotropic effects of statins and their beneficial effects in humans with CHF make statins promising therapeutic agents for the treatment of cardiac disease in dogs. This preliminary study demonstrated good tolerability of clinically relevant dosages of atorvastatin in healthy dogs and dogs with CHF. Future prospective studies are needed to evaluate the potential clinical benefits of statin administration in dogs with cardiac disease.

Acknowledgments

The authors thank Barbara Brewer for her assistance in data collection for this study, and Katie Cyr and IDEXX Laboratories for support of shipping and analysis of NT-proBNP samples.

This study was supported by an ACVIM Cardiology Resident Research Grant, the Tufts Cummings School of Veterinary Medicine Companion Animal Health Fund, and the Barkley Fund.

Conflict of Interest Declaration: Authors disclose no conflict of interest.

Footnotes

  1. 1

    Clinical Pathology Laboratory, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA

  2. 2

    Hewlett Packard, Wilmington, DE

  3. 3

    Lipitor; Pfizer Inc, New York, NY

  4. 4

    Tri-Delta Phase, Canine CRP assay; Tridelta Diagnostics Inc, Morris Plains, NJ

  5. 5

    Parks Ultrasonic Doppler Flow Detector Model 811-B; Parks Medical Electronics, Inc, Aloha, OR

  6. 6

    Lipid Metabolism Laboratory, Jean Mayer-USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA

  7. 7

    Cardiopet proBNP test; IDEXX Laboratories, Inc, Westbrook, ME

  8. 8

    Agilent 6890 Series GC and an Agilent 5973N Mass Selective Detector, Mayo School of Medicine and Mayo Clinic, Rochester, MN

  9. 9

    SPSS 17.0; SPSS, Chicago, IL

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