Right Ventricular Cardiomyopathy in the Rat - Is There an Association with Gavage?

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Right Ventricular Cardiomyopathy In The Rat
- Is There An Association With Gavage?
GA Willson1, RA Miller1 and D Malarkey2
1Experimental Pathology Laboratories, Inc. P.O. Box 12766, RTP, NC 27709, 2Cellular and Molecular
Pathology Branch, National Toxicology Program, National Institute of Environmental Health Sciences,
P.O. Box 12233, RTP, NC 27709
Figure 3
The histopathological examination of the heart in rodent toxicity
studies is an important endpoint. Spontaneous cardiomyopathy in
the Sprague Dawley (SD) and F344/N rats may interfere with
interpretation of treatment-related cardiotoxicity since spontaneous
lesions may overlap morphologically with lesions associated with
toxic effects.
There has been concern that some cardiomyopathy, observed in
the right ventricular epicardium, may be uniquely positioned,
dorsally, and possibly related to the gavage administration
technique.
Hearts were evaluated in control male Harlan Sprague Dawley rats
(gavage = 1 group, non-gavage = 4 groups; with 10 per group) and
control male F344/N rats (gavage = 10 groups, non-gavage = 10
groups; with mostly 10 per group). H&E sections of over 200 hearts
from 90-day studies were evaluated for lesions in the right
ventricle.
The percentage of gavaged SD rats with cardiomyopathy was 20%
with an average severity of 1.5. The non-gavaged SD rats
percentage affected was 25% with a mean severity of 1.2. The
gavaged F344/N rat percentage with cardiomyopathy was 28%
with a mean severity of 1.25. The non-gavaged F344/N rat
percentage with cardiomyopathy was 26% with a mean severity of
1.33.
The observed cardiomyopathy was similar in HSD and F344 male
rats. Morphologically it was the same regardless of the dose
administration modality. This epicardial and subepicardial lesion
was characterized by a minimal to mild, focal and multifocal,
infiltrate of mononuclear inflammatory cells and variable degrees of
fibrosis. Occasionally, there was only a thin fibrous connective
tissue scaffold with few inflammatory cells along the epicardium.
Occasional neutrophils and myocardial necrosis were present
within the lesions. The lesions generally occurred along the dorsal
one half of epicardium of the heart (towards the base) of the right
ventricle.
In this sample set of control male rats, it is apparent that this
epicardial lesion is a spontaneous lesion. The lesion was similar in
incidence and severity in HSD and F344 male rats and not affected
by the modality of exposure. In this series of rats it appears to be
unrelated to the gavage technique of exposure.
Table 3. Harlan Sprague Dawley Male Rats Incidence and
Severity of Right Ventricular Cardiomyopathy
The gavage male rats had an incidence of cardiomyopathy of 20%
and a mean severity of 1.5.
The non-gavage males had an overall incidence of 25% with an
overall mean severity of 1.2.
Table 4. F344 Male Rats Incidence and Severity of Right
Ventricular Cardiomyopathy
The gavage male rats had an overall incidence of cardiomyopathy
of 28% and a mean severity of 1.25.
The non-gavage males had an overall incidence of 26% with an
overall mean severity of 1.33.
The character and pattern of this cardiomyopathy was
morphologically similar in HSD and F344 male rats and presented
no difference among any of the dose administration modalities.
This epicardial and subepicardial lesion was characterized by a
minimal to mild, focal and multifocal, infiltrate of mononuclear
inflammatory cells and variable degrees of fibrosis. Occasionally,
there was only a scant fibrous connective tissue scaffold with few
inflammatory cells along the epicardium. Occasional neutrophils
and myocardial necrosis were present within the lesions. The
lesions generally occurred along the dorsal one half of epicardium
of the heart (towards the base) of the right ventricle.
Figure 2
Results
In an effort to assist the CardioVascular Specialty Interest Group
(CVSIG) within STP with their effort to harmonize the diagnostic
approach for cardiomyopathy in the rat, the following evaluation
was conducted.
In rodents cardiomyopathy is a spontaneous lesion of
undetermined etiology. It is more common in male rats although it
also occurs in females. It is evident in young rats (Chanut et. al.),
and the incidence and severity typically increases in incidence with
age (Mackenzie 1990). Cardiomyopathy occurs throughout the
heart with a spectrum of morphologies ranging from individual
degenerative/necrotic myofibers to larger areas of myocardial
degeneration/necrosis with varying quantities of lymphohistiocytic
inflammatory cell infiltrates and fibrosis (Jokinen et. al, 2011;
Chanut et. al, 2013). Because of this broad morphological range
and the fact that the heart has a limited injury response repertoire,
subtle treatment-related lesions may appear histologically similar to
cardiomyopathy in the rat (Greaves P., 2000; Ruben Z. et. al,
2000). Lesions may be due to a compound causing injury via a
similar mechanism and/or exacerbation of cardiomyopathy
(Jokinen et. al, 2011).
Introduction
Figure 1
Figure 4
References
This investigation was performed to assess whether or not epicardial
and subepicardial lesions of the right ventricle may be related to the
gavage administration technique. Two rat strains were investigated -
Harlan Sprague Dawley and F344 rats. All studies were conducted for
the National Toxicology Program (NTP) at study laboratories and the
studies commenced between 1994 and 2009.
Control male groups of Harlan Sprague Dawley (HSD) rats from 90-
day (subchronic) studies were identified. There was one gavage study
and four non-gavage studies (1 inhalation, 3 feeding) evaluated.
There were ten male rats per study group (Table 1).
Table 1. Study design (HSD rats)
Control male groups of F344/N rats from 90-day (subchronic) studies
were evaluated. Ten gavage studies and ten non-gavage studies (2
skin painting, 2 feeding, 3 water and 3 inhalation) were identified and
all available slides from the control males were evaluated.
Table 2. Study Design (F344/N rats)
H&E sections of hearts from each animal were evaluated for lesions in
the right ventricular epicardial and subepicardial location. The
cardiomyopathy was graded minimal when subtle and mild when
obvious. Twenty-five subchronic studies were selected for review.
The start dates for these studies were between 1994-2009.
Methods
Abstract
Right Ventricular Cardiomyopathy with 4x Objective. This
demonstrates the typical location of the lesions of interest, typically
occurring in the epicardial and subepicardial locations in the dorsal
(upper) portion of the heart. This epicardial and subepicardial lesion
was characterized by a minimal to mild, focal and multifocal, infiltrate
of mononuclear inflammatory cells and variable degrees of fibrosis.
Occasional neutrophils and myocardial necrosis were present within
the lesions.
Right Ventricular Cardiomyopathy with 10x Objective. This epicardial
and subepicardial lesion was characterized by a minimal to mild, focal
and multifocal, infiltrate of mononuclear inflammatory cells and
variable degrees of fibrosis. Occasional neutrophils and myocardial
necrosis were present within the lesions.
Right Ventricular Cardiomyopathy with 20x Objective. This epicardial
and subepicardial lesion was characterized by a minimal to mild, focal
and multifocal, infiltrate of mononuclear inflammatory cells and
variable degrees of fibrosis. Occasional neutrophils and myocardial
necrosis were present within the lesions.
Right Ventricular Cardiomyopathy with 40x Objective. This epicardial
and subepicardial lesion was characterized by a minimal to mild, focal
and multifocal, infiltrate of mononuclear inflammatory cells and
variable degrees of fibrosis. Occasional neutrophils and myocardial
necrosis were present within the lesions.
In these selected groups of control male rats, it is
apparent that this epicardial lesion is a spontaneous
lesion. The lesion was similar in incidence and severity in
both HSD and F344 male rats and was not affected by the
modalities of exposure. Right ventricular cardiomyopathy
is unrelated to the gavage method of exposure in this
series of animals.
Conclusion
Length of Study
(days)
Study designation
Route of
exposure
Number of control
male rats
examined
92 Study A Gavage 10
92 Study B Inhalation 10
92 Study C Feed 10
92 Study D Feed 10
92 Study E Feed 10
Length of Study
(days)
Study designation
Route of
exposure
Number of control
male rats
examined
94 Study F Gavage 9
94 Study G Gavage 10
93 Study H Gavage 10
93 Study I Gavage 10
93 Study J Gavage 10
94 Study K Gavage 10
93 Study L Gavage 9
93 Study M Gavage 10
91/150 Study N Gavage 12
93 Study O Gavage 10
92 Study P Feed 10
92 Study Q Feed 10
93 Study R Skin 10
93 Study S Skin 10
93 Study T Inhalation 10
93 Study U Inhalation 10
93 Study V Inhalation 10
93 Study W Drinking water 10
15/91/150 Study X Drinking water 14
93 Study Y Drinking water 10
Gavage Study Incidence of Right Ventricle
Cardiomyopathy
Study A 2/10 (1 minimal and 1 mild)
Non-Gavage studies Incidence of Right Ventricle
Cardiomyopathy
Study B (Inhalation) 3/10 (2 minimal, 1 mild)
Study C (Feed) 2/10 (2 minimal)
Study D (Feed) 4/10 (3 minimal, 1 mild)
Study E (Feed) 1/10 (1 minimal)
Gavage Studies Incidence of Right Ventricle
Cardiomyopathy
Study F 2/9 (2 minimal)
Study G 5/10 (2 minimal, 3 mild)
Study H 1/10 (1 minimal)
Study I 1/10 (1 minimal)
Study J 5/10 (4 minimal, 1 mild)
Study K 1/10 (1 minimal)
Study L 1/9 (1 minimal)
Study M 4/10 (4 minimal)
Study N 1/12 (1 minimal)
Study O 7/10 (4 minimal, 3 mild)
Non-Gavage Studies Incidence of Right Ventricle
Cardiomyopathy
Study P (Feed) 4/10 (2 minimal, 2 mild)
Study Q (Feed) 1/10 (1 minimal)
Study R (Skin) 1/10 (1 mild)
Study S (Skin) 2/10 (2 minimal)
Study T (Inhalation) 2/10 (2 mild)
Study U (Inhalation) 2/10 (2 minimal)
Study V (Inhalation) 3/10 (2 minimal, 1 mild)
Study W (Water) 4/10 (4 minimal)
Study X (Water) 2/14 (2 minimal)
Study Y (Water) 6/10 (3 minimal, 3 mild)
Figures 1-4. Illustrate a variety of lesion appearances of cardiomyopathy taken at four different magnifications. The illustrated lesions from the HSD gavage
study, HSD Feed, and F344 Feed study were considered mild and the lesion from the illustrated F344 inhalation study was considered minimal.
Figures
F344 Inhalation Study HSD Gavage Study
F344 Feed Study HSD Feed Study
F344 Inhalation Study HSD Gavage Study
F344 Feed Study HSD Feed Study
F344 Inhalation Study HSD Gavage Study
F344 Feed Study HSD Feed Study
F344 Inhalation Study HSD Gavage Study
F344 Feed Study HSD Feed Study
Thanks to Michelle McCrimmon, Kim Pernicka, Maureen Puccini and
Emily Singletary of EPL for photography and technical assistance and
to Lois Wyrick of Image Associates for the graphic design of this
poster.
Acknowledgements