Abstract
The Göttingen minipig is gaining increasing popularity as a nonrodent species in nonclinical testing. The Göttingen minipig is easy to handle; has many anatomical and physiological similarities to man; and causes fewer ethical concerns than usage of the traditional nonrodent species, nonhuman primates, and dogs. The increasing usage of the Göttingen minipig has raised the need of appropriate background data. This article summarizes the background pathology of 835 untreated control Göttingen minipigs of both sexes used at CiToxLAB Scantox A/S during the period of 1995 to 2007.
Introduction
The popularity of the minipig in pharmacology, pharmacokinetic, and toxicological safety evaluation studies of new pharmaceuticals and biopharmaceutical products has increased rapidly over recent years. An increasing appreciation of the similarities between man and the pig, including the Göttingen minipig, with respect to the structure of the skin, gastrointestinal tract, cardiovascular system, urogenital system, and metabolism of xenobiotics (Bode et al. 2010; Swindle et al. 2012) is the principal reasons for this. Furthermore, the increased ethical concerns related to the use of other nonrodent species such as nonhuman primates and dogs in research have contributed to the increased interest in minipigs. For these reasons, over the recent years, an increasing amount of background data for Göttingen minipigs have been accumulated. The existence of significant amounts of background data, from a regulatory point of view as well as from a GLP (Good Laboratory Practice) perspective, provides a strong support for the use of this species in mainstream research. At CiToxLAB Scantox A/S in Denmark, we have worked with Göttingen minipigs for more than 25 years. To our knowledge, no comprehensive overview of the background pathology in Göttingen minipigs has yet been published.
The most obvious starting point when considering the Göttingen minipig is in the development of dermal products due to the similarities of pig and human skin. However, one soon comes to realize that this species is a good alternative for all routes of administration and durations of studies when any or all of the traditional species are found to be unsuitable. All of the standard measurements (ophthalmoscopy, electrocardiography, etc.) can be employed in minipigs. Blood samples are readily available from the jugular vein or from the bijugular trunk. As the minipig lacks any sizable peripheral vein, repeated intravenous dosing is only possible using surgically implanted catheters.
In addition, to routine toxicology studies, the Göttingen minipig can be used as an alternative species in performing embryofetal reproductive toxicology studies when other species are not found to be suitable—the early onset of sexual maturity and large litter size offer a particular advantage in these type of studies.
In addition, a number of disease models have been developed in the minipig to specifically address, for example, Parkinson’s disease, atherosclerosis, or diabetes (type 1 and type 2) research.
The objective of this article is to present data from control Göttingen minipigs in studies conducted at CiToxLAB Scantox A/S over a 12-year period from 1995 to 2007.
Materials and Methods
The Göttingen minipig was developed as a breed at the University of Göttingen (Germany), originating from a crossing between the Minnesota minipig, obtained from the Hormel Institute in Austin (Austin, MN) by the Institut für Tierzucht und Haustiergenetik in 1961 to 1962, and the Vietnamese potbelly swine, obtained from German Zoos. In this crossing, a colored miniature swine was used in a backcrossing with the German Landrace. The offspring of the backcrossing, the white line of the Göttingen minipig combined the type and temperament of the Minnesota minipig with the fertility of the Vietnamese potbelly pig and the white phenotype of the German Landrace. A full pedigree of the animals is kept at the University of Göttingen, and selection is based on keeping the colony outbred. Genetic management is required in order to minimize inbreeding and drift and to maintain the genetic integrity of the population. The genetics for the entire breeding population are still managed in Göttingen, and all breeding data date back to the 1960s when the Göttingen minipig was developed.
The entire breeding population for Göttingen minipigs is found in 3 physical locations (Dalmose, Denmark; Göttingen, Germany; and North Rose, NY). Despite separation into subpopulations, the Göttingen minipig population is genetically coherent. Since 1992, the Göttingen minipig has been bred under full barrier conditions in Denmark at the facility in Dalmose, Ellegaard Göttingen Minipigs. All animals used to generate the present background data originate from Dalmose.
In general, being held under strict barrier conditions, the Ellegaard Göttingen minipig does not share most of the common diseases found in conventional and SPF (Specific Pathogen Free) domestic swine. In facilities keeping domestic swine as well as minipigs, precautions should be made to keep these strictly separated. The Göttingen minipig is microbiologically defined on a regular basis being tested for a number of diseases according to the recommendations of the Federation of European Laboratory Animal Science Associations (FELASA; for details, please consult the Ellegaard Göttingen Minipigs website, www.minipigs.dk).
The background data presented in this article were generated from control Göttingen minipigs included in nonclinical toxicity studies. The control animals were either untreated or dosed with placebo. The duration of the studies ranged from 2 weeks to 1 year. The route of administration was oral, dermal, subcutaneous, or intravenous.
Upon arrival at our facility, a pretreatment period of 3 weeks (including an acclimatization period of 5 days) was allowed during which the animals were observed daily in order to reject animals in poor condition. The studies took place in animal rooms provided with filtered air at a temperature of 21°C ± 3°C and relative humidity of 55% ± 15%. The ventilation system gave 10 to 15 air changes per hour. The rooms were illuminated to give a cycle of 12-hr light and 12-hr darkness. The animals were housed individually in floor pens of at least 2 m2 with sawdust as bedding. Before the animals arrived, the animal rooms were cleaned and disinfected. During the studies, the animal rooms and the pens were washed regularly and rinsed with water. An SDS (Special Dietary Services) minipig diet was offered twice daily. A supply of autoclaved hay was given daily. The animals had ad libitum access to domestic quality drinking water.
Göttingen minipigs, especially the females, must be fed a restricted diet to control their growth. The exact dietary requirements are influenced by a variety of factors that need to be taken into account when designing a suitable dietary regimen. Factors that influence the requirements include age, weight, gender, health status, activity, singular/group housing, room temperature, and velocity (number of air changes per hour; www.minipigs.dk).
Histopathological data were collected from 417 male and 418 female Göttingen minipigs from Ellegaard Göttingen Minipigs, Dalmose, Denmark.
The histopathological data have been tabulated by route of administration and length of study. The 12-year period from 1995 to 2007 has been subdivided into a 5-year and a 7-year period. The reason for dividing the data material into 2 groups of different sizes is that the material was previously presented on a conference being divided into 2 groups of 5 years each. However, in the making of this article, the tables have been updated to include histopathological data from an addtional 2 years in order to include additional background data. Furthermore, based on increasing experience with Göttingen minipigs at our facility, the diagnostic criteria and the threshold for diagnosis of minor lesions have changed somewhat over time but have more or less been constant since 2000. All background lesions recorded in control Göttingen minipigs at CitoxLAB Scantox during this period of time have been tabulated. In the following Results section, most of the lesions are presented.
All the observations have been graded or marked as present according to the following grading system:
Histological alterations were graded on a 5-grade system:
Grade 1: Minimal/very few/very small. Grade 2: Slight/few/small. Grade 3: Moderate/moderate number/moderate size. Grade 4: Marked/many/large. Grade 5: Massive/extensive number/extensive size. Present: Finding present/severity not scored.
In many organs, the diagnosis of infiltration of inflammatory cells as well as a diagnosis of inflammation have been used. The former term refers to an infiltration of inflammatory cells without the presence of tissue damage, whereas the latter term is used in cases where the inflammatory cells are accompanied by evidence of tissue damage like edema, hemorrhage, and/or necrosis.
Results
1. Brain cerebrum/cerebellum/pons/medulla (Supplemental Table S1)
Minimal focal gliosis and minimal focal infiltration of mononuclear cells/inflammatory cells were described in a few animals. Focal minimal mineralization in the meninges is quite often observed in the minipigs, but it is not included in the incidence table, since we normally do not record such mineralization in our laboratory.
2. Eyes (including optic nerve; Supplemental Table S2)
Focal slight lentic degeneration has been observed in 1 male and 1 female, focal slight corneal hyperplasia in 1 female, and focal minimal inflammation at the corneal/scleral junction in another female.
3. Lacrimal glands (Supplemental Table S3)
Focal minimal to slight infiltration of mononuclear cells is occasionally observed in these glands.
4. Thymus (Supplemental Table S4)
The thymus of young Göttingen minipigs extends from the cranial part of the thoracic cavity into the neck to reach the level of the larynx. In older minipigs, some thymic tissue usually remains in both the neck and the thorax.
Minimal to moderate thymic atrophy has been recorded in a low number of animals. The atrophy is primarily cortical. Even at the end of a 1-year study, no signs of involution would usually be expected in a Göttingen minipig. In general, the incidence of spontaneous thymic cortical atrophy is very low in the Göttingen minipig compared to the other commonly used laboratory species.
Interlobular hemorrhage/inflammation as well as hemorrhage/inflammation in the adnexal tissues arising in relation to the blood sampling procedure are commonly observed in toxicity studies.
5. Spleen (Supplemental Table S5)
Focal minimal fibrinoid necrotizing arteritis in a single small size artery has been observed. Slightly to moderately increased extramedullary hematopoiesis and slightly increased numbers of macrophages with a focal distribution have occasionally been found, especially in young animals used in short-term studies.
6. Sternum
A case of focal minimal chronic inflammation (male, 1/151, 2 + 4 weeks studies, 2000–2007), slight focal fibrosis (female, 1/69, 13 weeks study, 2000–2007), and slight focal osseous hyperplasia (female, 1/41, 6–12 months studies, 2000–2007), respectively, have been reported.
7. Mandibular lymph node (Supplemental Table S6)
Minimal to slight abscess formation, often delineated by a prominent capsule, has been observed in some animals (Figure 1). Moderate diffuse amyloidosis, slight focal granulomatous inflammation, and minimal to moderate sinusoidal histiocytosis have each been diagnosed in 1 or 2 animals.
Mandibular lymph node, abscess, H&E, 10×. H&E = hematoxylin and eosin.
8. Mesenteric lymph node (Supplemental Table S7)
Minimal to moderate lymphadenitis has been described in a few animals. Minimal to moderate arteritis/periarteritis has similarly been observed in a few animals, either in the lymph node or in the mesenteric vessels. Varying numbers of eosinophilic granulocytes are commonly present in the sinus of the lymph nodes and are not reported unless a relation to treatment is suspected.
9. Heart (Supplemental Table S8)
A single incidence of a defect in the septum of the ventricles was observed in a male from a 6-month oral study. The abnormality was found at postmortem and confirmed during the microscopic examination.
Slight focal myocarditis (including myocardial necrosis), focal minimal pericarditis, minimal to slight focal epicardial/subepicardial edema, minimal focal fibrosis, minimal focal hemorrhage, minimal to slight arteritis/periarteritis, focal mineralization, and focal infiltration of mononuclear cells were each reported in a single or a few animals in the data set.
In intravenous infusion studies, the focal subacute endocarditis and thickening of the intima/endocardium in the right atrium are considered to be related to the method of treatment representing a local irritative effect at the tip of the intravenous catheter.
10. Aorta arch/thoracic (Supplemental Table S9)
Minimal to slight focal serosal proliferation is occasionally observed in the aortic arch.
11. Larynx (Supplemental Table S10)
Minimal to slight focal infiltration of inflammatory cells and a single incidence of a focal fibrinoid necrotizing arteritis have been observed.
12. Trachea
Minimal submucosal inflammation has been described (male, 1/151, 2 + 4 weeks studies, 2000–2007). Peritracheal hemorrhage/inflammation arising during the blood sampling procedure is often observed in toxicity studies.
13. Lungs (Supplemental Table S11)
The findings in the lungs in the Göttingen minipig are in general relatively few and subtle. The most common findings in the lungs are minimal numbers of granulomas and focal infiltration of alveolar macrophages (Figure 2). Minimal focal mineralization can occur in association with the alveolar macrophages. Pneumonia (broncho, interstitial, or granulomatous) of varying severity is observed occasionally as well as focal minimal infiltration of mixed inflammatory cells, pleuritis, or fibrosis. Minimal to slight arteritis/periarteritis and thrombi have been sporadic observations; in studies with intravenous dosing, thromboembolic pneumonia is seen with an increased frequency related to the intravenous route of administration.
14. Tongue (Supplemental Table S12)
Most often lesions in the tongue are found in the studies with oral administration. The lesions are linked to mechanical damage, as the minipig is prone to biting the tongue in relation to the dosing procedure. Dosing in oral studies is most often done by gavage. The findings in the tongue include focal slight to moderate erosions/ulcerations (Figure 3) and minimal to slight focal myositis, occasionally associated with focal necrosis. Single incidences of minimal epithelial hyperplasia and epithelial vacuolation have been described. It is worth noting that, in our experience, the basal parts of the epithelium of the tongue appear quite basophilic often with vacuolation and swollen cells; focal differences in this basophilia can be present within the same animal and care should be taken not to misinterpret this as a treatment-related finding.
15. Salivary glands (parotid, submandibular, sublingual; Supplemental Table S13)
Focal minimal mineralization in relation to the ducts can be observed in the sublingual (Figure 4) and the submandibular glands. Focal infiltration of primarily mononuclear cells can be found in all glands. Single incidences of focal ductular hyperplasia/fibrosis and minimal focal acinar atrophy have been recorded.
16. Esophagus (Supplemental Table S14)
Minimal focal infiltration of mononuclear cells/inflammatory cells has been described in a low number of animals. Periesophageal hemorrhage/inflammation occurring as a result of the blood sampling procedure is often observed in toxicity studies.
17. Stomach nonglandular (Supplemental Table S15)
Minimal to slight focal erosions and minimal focal accumulation of neutrophils/inflammatory cells have been observed in some animals. Moderate to marked ulceration have been found in 2 females, respectively. Minimal fibrinoid necrotizing arteritis has been recorded in a few animals. Keratin cysts can occasionally be observed.
18. Stomach glandular (Supplemental Table S16)
Slight to moderate focal ulceration and minimal to slight erosions have been observed in a few animals of both sexes (Figure 5). Minimal focal inflammation and focal infiltration of neutrophilic or eosinophilic granulocytes can be found with a low incidence. Focal fibrinoid necrotizing arteritis, focal glandular atrophy, and a cyst in pars cardia have been described in a few animals.
19. Duodenum (Supplemental Table S17)
Focal minimal to slight erosions, focal minimal to slight mucosal inflammation, and villous atrophy were observed in 1 or 2 animals. Furthermore, single cases of focal fibrosis, decreased number of goblet cells, focal arteritis, and focal phlebitis have been described.
20. Jejunum (Supplemental Table S18)
Minimal to marked mucosal inflammation and minimal to slight villous atrophy have been observed in some animals (Figure 6).
21. Ileum (Supplemental Table S19)
Minimal to moderate mucosal inflammation and minimal to marked villous atrophy have been observed in some animals. Minimal to slight focal peritonitis was found in a few animals and single incidences of slight ulcerations, minimal focal fibrosis in the muscular layer, slight focal granuloma in the mesentery, and minimal focal infiltration of inflammatory cells have been described.
22. Cecum (Supplemental Table S20)
Minimal to moderate mucosal inflammation has been described in some animals. A single incidence of a minimal focal peritonitis was found.
23. Colon (Supplemental Table S21)
Minimal to slight mucosal inflammation has been described in some animals. Minimal peritonitis was found in a few animals, and minimal submucosal edema and minimal focal epithelial hyperplasia have each been observed in a single animal.
24. Rectum
Minimal mucosal inflammation has been observed in a few animals (male, 1/82, 2 + 4 weeks studies, 1995–2000), (male, 1/46, 13 weeks study, 2000–2007) and minimal chronic arteritis was found in a single animal (female, 1/41, 6–12 months studies, 2000–2007).
25. Liver (Supplemental Table S22)
Spontaneous changes in the liver have been reported with a very low incidence. They include minimal to slight focal parenchymal necrosis, minimal focal single cell necrosis, minimal to slight focal infiltration of mononuclear cells or mixed inflammatory cells, minimal to moderate vacuolation of the hepatocytes, minimal to slight focal extramedullary hematopoiesis, and minimal to moderate focal fibrosis (subcapsular and/or interlobular). Vast amounts of interlobular connective tissue are characteristic for the minipig similar to that for the domestic pig.
26. Gall bladder (Supplemental Table S23)
In our spontaneous background material of Göttingen minipigs, one of the most striking changes is a fairly high incidence of cholecystitis. Cholecystitis was primarily described as acute, subacute, chronic, or chronic active with a severity ranging from moderate to massive (Figures 7 and 8). The acute cases of cholecystitis were often characterized as necrotizing. In general, no clinical signs are observed in animals diagnosed with cholecystitis. To our knowledge, the etiology of the cholecystitis in Göttingen minipigs remains unclear.
Gallbladder, necrotizing cholecystitis, H&E 2½×. H&E = hematoxylin and eosin.
Furthermore, a few cases of hypoplasia or aplasia of the gall bladder have been observed (Figure 9). At necropsy, it is in our experience prudent to sample/inspect the gall bladder as one of the first steps upon opening the abdominal cavity.
27. Pancreas (Supplemental Table S24)
Minimal focal interstitial hemorrhage and minimal focal infiltration of mononuclear cells were present in a few animals. Minimal focal arteritis/periarteritis has been observed in a single animal.
28. Kidneys (Supplemental Table S25)
In general, the kidneys of the Göttingen minipigs are found to have a low number of incidental findings of a low severity. Minimal focal interstitial nephritis, a single incidence of minimal glomerulonephritis, and minimal to slight focal inflammation were observed in a few animals. Minimal to moderate glomerulosclerosis is occasionally observed and most often located at the corticomedullary junction. Minimal to slight (rarely moderate) focal tubular basophilia is a relatively common finding, sometimes associated with tubular dilation and/or cellular debris. Minimal to slight focal fibrosis was described in a few animals. Minimal arteritis, often fibrinoid necrotizing, minimal periarteritis, and minimal phlebitis can occasionally be observed, most often just in a single artery/vein (Figure 10). Minimal to slight interstitial infiltration of mononuclear cells and/or mixed inflammatory cells are quite common findings in the kidney. Focal infiltration of eosinophilic granulocytes has been found in the pelvic region in 2 females. Minimal focal mineralization is commonly seen in the papilla and rarely in other locations. Cyst/cysts in the medulla or cortex are observed once in a while. Moderate congestion in the papilla has been described in a single animal. The cortex of the juvenile minipig has a high number of small dense basophilic immature glomeruli (Figure 11).
29. Urinary bladder (Supplemental Table S26)
In the urinary bladder, minimal to slight focal cellular infiltration (mononuclear/mixed inflammatory cells) as well as congestion of the submucosal blood vessels are the main findings. In addition to this, a few cases of serosal abscesses, minimal arteritis/periarteritis, and moderate edema of the muscular layer have been reported.
30. Adrenals (Supplemental Table S27)
In the adrenals, minimally to slightly increased cortical vacuolation and minimal to slight focal infiltration of mononuclear cells/extramedullary hematopoiesis have been described with a low incidence. A single case of focal cortical hyperplasia has been observed.
31. Parathyroids (Supplemental Table S28)
In Göttingen minipigs (as it is the case in domestic swine), the parathyroid is not located in relation to the thyroid gland but cranial in the cervical thymus often just caudal to the hyoid bone. This poses a challenge at necropsy; however, at our laboratory, we have extensive experience in locating the parathyroids resulting in a very high success rate (estimated >95%). The only findings reported in the parathyroids were cysts as well as minimal cellular vacuolation.
32. Pituitary (Supplemental Table S29)
In the pituitary, the following lesions have been observed with an extremely low incidence (1–2 cases per lesion): cysts in the pars distalis, minimal focal mineralization, minimal presence of vacuolated cells in the pars distalis, and minimal focal infiltration of mononuclear cells. Dystrophic mineralization (diameter less than 2–3 pars distalis cells) is commonly seen but is considered to be below the threshold of reporting.
33. Thyroids (Supplemental Table S30)
In the thyroids, ultimobranchial cysts are occasionally observed. In addition to this, single incidences of focal infiltration of mononuclear cells as well as focal squamous metaplasia have been reported. Hemorrhage and inflammation in the adnexal tissues are common findings related to the procedure of blood sampling and have not been included in the incidence table.
34. Testes (Supplemental Table S31)
Being sexually mature at an age of 4 to 6 months, the Göttingen minipig offers a significant advantage compared to the conventional laboratory nonrodent species, as the animals included in toxicity testing should have reached sexual maturity at the start of the study (Swindle et al. 2012).
Tubular hypoplasia/atrophy is by far the most common incidental background finding in the testes of male Göttingen minipigs. Tubular hypoplasia/atrophy is characterized by a variable reduction in the number of germ cells and sertoli cells, both of which can be vacuolated and covers the entire range of severity from merely a few tubules affected to all tubules being affected with no spermatogenesis taking place (Figures 12 and 13). Based on the present data set, the spontaneous incidence of tubular hypoplasia/atrophy does not appear to increase with increasing age of the Göttingen minipig.
Testis, tubular, hypoplasia atrophy H&E 20×. H&E = hematoxylin and eosin.
In our experience, the incidence of the tubular hypoplasia/atrophy has been decreasing during recent years.
A few cases of sperm granulomas and cysts have been described. In a recent study (not included in the incidence table), a spontaneous case of a unilateral interstitial cell adenoma has been reported.
It should be noted that the interstitial cells in the testes of Göttingen minipigs are prominent, so reporting of interstitial cell hyperplasia should be done with extreme care, as this could easily be overdiagnosed especially in cases of tubular hypoplasia/atrophy.
35. Epididymides (Supplemental Table S32)
Oligospermia and/or abnormal spermatids are reported commonly corresponding to the occurrence of tubular hypoplasia/atrophy in the testes. Granulomas and cysts have occasionally been observed. Inflammation and fibrinoid necrotizing arteritis are rare findings.
36. Prostate (Supplemental Table S33)
Varying types and degrees of inflammation are the most common findings in the prostate. A few cases of mineralization as well as a single case of hyperplasia have been observed.
37. Seminal vesicles
A single case of a minimal focal interstitial inflammation has been reported (male, 1/82, 2 + 4 weeks studies, 1995–2000). Likewise, minimal focal periarteritis/arteritis has been observed (male, 1/41, 6–12 months studies, 2000–2007).
38. Ovaries (Supplemental Table S34)
The sexual cycle of the female Göttingen minipig is considered to be comparable to that of domestic swine being polyestrous with a cycle span of 3 weeks. In our control material, very few background lesions have been identified in the female reproductive tract. In the ovaries, a few cases of minimal hemorrhage and hemorrhagic cysts have been found. Mineralization can commonly be seen especially in association with atretic follicles.
As a matter of interest, it should be mentioned that a well-defined benign teratoma has been recorded in the ovarian stroma of a single female minipig—this has not been included in the incidence table since it occurred in a treated animal.
39. Oviducts
One case of squamous metaplasia has been observed in the oviducts of a female Göttingen minipig (1/69, 13-week study, 2000–2007).
40. Uterus (including cervix)
Minimal focal hemorrhage has been reported (female, 1/151, 2 + 4 weeks studies, 2000–2007 as well as in 1/28, 6–12 months studies, 1995–2000).
41. Vagina
In the vagina, including the cervix, a single case of hypoplasia has been identified (female, 1/69, 13 weeks study, 2000–2007).
42. Mammary gland (Supplemental Table S35)
In the mammary glands, a minimal to slight focal inflammation, a minimal hemorrhage, a minimal focal infiltration of inflammatory cells, and a minimal intraductular fibrosis have been reported at a low incidence.
43. Skin (Supplemental Table S36)
One of the advantages of using the Göttingen minipigs in toxicity testing is the fact that the skin of the Göttingen minipigs closely resembles the human skin. This especially poses an advantage in dermal studies and wound healing studies. In general, the skin of the Göttingen minipig has very few spontaneous lesions. The main background lesions in the skin of Göttingen minipigs include minimal to marked focal crusts, minimal focal infiltration of mononuclear cells (primarily in the superficial dermis), minimal to slight edema (epidermal/dermal), epidermoid cysts, minimal to slight hyperkeratosis, minimal to moderate inflammation, minimal or marked acanthosis, minimal erosions, and minimal epidermal hyperplasia. Crusts are by far the most common finding (Figures 14 and 15).
Periocular hyper-/parakeratosis are commonly seen in the eye region as well as on the dorsal side of the neck and back. An involvement of Candida albicans in this lesion has been previously demonstrated (Bollen et al. 1998).
When considering dermal minipig studies, it should be taken into consideration that the thickness of the skin varies significantly depending on the location on the body, for example, the skin of the neck is quite thick compared to that of the back. In dermal studies performed at our facility, the skin of the back is the preferred option for dosing.
An immune complex–associated thrombocytopenic purpura syndrome has been described in sexually mature Göttingen minipigs and the basis of this condition has been reported to be a type III hypersensitivity (Carrasco et al. 2003). The syndrome, also called the hemorrhagic syndrome, has on a few occasions been manifest in Göttingen minipigs at CiToxLAB Scantox A/S. The necropsy findings in these cases were multiple pettichiae/ecchymosis in the skin, mucous membranes, and internal organs. Histopathologically, focal hemorrhages were observed. These data have not been included in the incidence tables.
44. Skeletal muscle (Supplemental Table S37)
In the skeletal muscle, minimal to moderate focal myositis, minimal to moderate focal necrosis of myofibers, minimal to slight focal infiltration of mononuclear cells, minimal focal mineralization, and minimal to slight focal presence of degenerating/regenerating myofibers have been observed. We have seen acute (hemorrhage, necrosis, and infiltration of neutrophilic granulocytes), subacute, and chronic (fibrosis, mineralization, and mononuclear cells) cases of myositis (Figure 16).
To our knowledge, the etiology of the myositis has not yet been elucidated, though dietary or hereditary causes have been speculated.
45. Femur/Tibia (Supplemental Table S38)
The only spontaneous lesion we have found in the femur/tibia of our control Göttingen minipigs within the period 1995 to 2007 has been minimal to marked serous atrophy of the adipose tissue in the bone marrow (Figure 17). This is a well-described lesion especially in male Göttingen minipigs (Bollen and Skydsgaard 2006). It is important to state that the minipigs showing this alteration are clinically unaffected. The etiology of the serous atrophy is nutritional factors, probably related to the employed restricted feeding regimen. Histopathologically, serous atrophy of the adipose tissue in the bone marrow is seen as atrophy of the adipocytes as well as decreased cell density of the hematopoietic cells in the bone marrow and accompanied by infiltration of acidic mucopolysaccharides.
Discussion/Conclusion
This article has presented an introduction to the spontaneous background findings in Göttingen minipigs used in preclinical toxicity testing at CitoxLAB Scantox A/S during the period 1995 to 2007.
During our work with the Göttingen minipigs, we have become familiar with the particular characteristics of this species. After having discussed the common background changes in the previous sections, we would like to highlight a few noteworthy features of the Göttingen minipig.
The thymus of young Göttingen minipigs extends from the cranial part of the thoracic cavity into the neck to reach the level of the larynx. In older minipigs, some thymic tissue usually remains in both the neck and the thorax. At the end of a 1-year study, no signs of age-related involution would usually be expected in a Göttingen minipig. In general, the incidence of spontaneous thymic cortical atrophy is very low in the Göttingen minipig compared to the other commonly used laboratory species. The morphology of the thymic cortical atrophy is similar to what is seen in normal age-related thymic involution primarily consisting of decreased numbers of lymphocytes in the cortex. The diagnosis of thymic cortical atrophy is used when the degree of thymic involution in an individual exceeds that of the majority of the population.
In toxicity studies involving routine blood sampling using the jugular veins, hemorrhage and inflammation in the adnexal tissues of mainly thymus, thyroids, esophagus, and trachea are commonly observed sequels to this procedure.
Increased extramedullary hematopoiesis in the red pulp of the spleen is mainly seen in juvenile animals as well as in short-term toxicity studies (at a lower incidence compared to the juvenile studies).
In intravenous studies, dosing is performed using intravenous catheters occasionally causing procedure-related changes primarily at the tip of the catheter in the cranial caval vein or in the right atrium if the tip of the catheter has been advanced too far to reach the heart (including thrombus formation at the intravenous infusion site, endothelial/endocardial thickening, and endocarditis). In cases of major thromboses, microthrombi might be found elsewhere, mainly in the lungs but also occasionally in the kidneys (glomeruli) and the liver.
The histopathological findings of spontaneous nature in the Göttingen minipig as described in this article are few and in general focal and mild. Characteristic spontaneous findings are found in the gallbladder (cholecystitis and hypoplasia/aplasia), skeletal muscle (myositis/myofiber necrosis), and adipose tissue (serous atrophy) in the bone marrow. The hemorrhagic syndrome characterized by widespread pettichiae/hemorrhages occurs with a very low incidence and has an unknown etiology.
Considering that mentioned earlier, we consider the Göttingen minipig to be suitable as an alternative nonrodent species in toxicity testing.
Supplemental Materials
Supplemental tables and figures can be found at http://tpx.sagepub.com/supplemental
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Footnotes
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Abbreviation
References
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