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Intracranial tumors in mice of two different strains maintained on fat enriched diets
Europ. J. CancerVol. 7, pp. 529-532. Pergamon Press 1971. Printed in Great Britain
Intracranial Tumors in Mice of Two Different Strains Maintained on Fat Enriched Diets* J. SZEPSENWOL Department of Anatomy, University of P. R. School of Medicine, San Juan, Puerto Rico A b s t r a c t - - T w o mice of BALB/c strain maintained on Purina chow supplemented with egg yolk developed, one at the age of 619 days and the other one at the age of 429 days, oligodendrogliomas originating from the cortex of the right hemisphere. The tumor of the first mouse invaded the interhemisphericfissure and extended to the brain stem and the posterior pole of the hemisphere. Two other mice of the T. M. strain, maintained on Purina chow supplemented with monoolein and cholesterol, and with lecithin and cholesterol, developedat the ages of 804 and 700 days respectively a fibrosarcoma associated with trigeminal nerve in the first case, and a brain-nerve cell tumor of the left hemisphere complicated by what appears to be a lymphoma in the second case. None of the control mice of the two strains developedintracranial tumors.
INTRODUCTION
strain, maintained on Purina chow supplemented with raw egg yolk, and the other two in mice of the T. M. strain maintained on Purina chow supplemented with vegetable lipids.
NEOPLASMS of the nervous system have been induced in mice and rats by direct application of carcinogenic hydrocarbons such as benzpyrene, dibenzanthracene, dimethylbenzanthracene and methylcholanthrene. T h e y have also been obtained by administration, via the digestive tube, of 2-acetylaminofluorene [1]. More recently, various nitrosamine compounds, administered either intravenously of per os, were found to induce in rodents tumors of the central and peripheral nervous systems [2]. O n the other hand, it was found that mice maintained on Purina chow supplemented with various lipids develop tumors of the cerebral cortex consisting entirely of differentiated nerve cells [3]. The present study is a report of 4 intracranial tumors, of a different nature, found in mice of two different strains maintained, as the above mentioned mice, on fat enriched diets. T w o of these tumors were in mice of the BALB/c
MATERIAL AND METHODS
The BALB/c mice? have been maintained on Purina chow supplemented with raw egg yolk (one egg yolk per 25-30 mice daily), while for the mice of the T. M. strain, like in previous experiments [3], the Purina chow was supplemented with small amounts of vegetable oil. In both cases, the mice were placed on the above diets at the age of 4 weeks, they were bred and their offspring maintained on the same diets. Mice of both strains maintained on Purina chow only, without supplements, were used as controls. The mice were killed when they were rapidly loosing weight. The skull was opened and the brain carefully examined. Those with tumors were fixed with Bouin's fluid, or with a 10% solution of formaldehyde, embedded in paraffin, sectioned serially and stained with hematoxylin and eosin. In some cases other staining techniques were used.
Accepted 21 May 1971. * Supported by General Research Grant FR 5419-04. t The original BALB/c mice were supplied by H. B. Andervont. Nat. Cancer Inst. Bethesda, MD. to whom we are greatly indebted. 529
530
J. Szepsenwol RESULTS
The two BALB/c mice with brain tumors (tumors 1 and 2) were both males; one was 619 and the other 429 days old. They were both on the Purina chow supplemented with egg yolk from the day they were born: they were offspring of mice maintained on the same diet. Macroscopically, the brain of the mouse 619 days old had a nodule projecting from the right hemisphere into the interhemispheric fissure and delimited laterally by a depressed area (Fig. 1). This nodule, as seen in sections, was actually not the tumor; it consisted of normal hemispheric tissue. It was separated from the rest of the cortex by a growing mass of cells extending from the depressed area of the hemisphere (Fig. 2) along the interhemispheric fissure to the brain stem and the inferior surface of the hemisphere (Fig. 3), and having all the characteristics of an oligodendroglioma. It was cellular and the cells had relatively large dark nuclei and clear cytoplasm. M a n y of them were in mitosis and some of the mitotic figures were abnormal (Fig. 4). The second BALB/c mouse, 429 days old, presented a large depressed area on the lateral surface of the right hemisphere with a small whitish nodule emerging from its posterosuperior end (Fig. 5). In microscopic sections this part of the hemisphere consisted, like tumor i, of a mass of cells with large dark nuclei and clear cytoplasm (Fig. 6). Mitotic figures, some of which were abnormal, were abundant. This, as in the previous case, was without any doubt an oligodendroglioma. O f the two intracranial tumors (tumors 3 and 4) in mice of the T. M. strain one was in a female 804 days old (maintained on Purina chow supplemented with monoolein and cholesterol) and the other one in a female 700 days old (maintained on Purina chow supplemented with lecithin and cholesterol). They were both offspring of mice maintained on the same diets. T u m o r 3, in the mouse on the diet supplemented with monoolein and cholesterol, appeared as a large mass on the trajectory of the left trigeminal nerve (Fig. 7). It was continuous with the brain stem, with the lateral surface of the hemisphere, which was compressed and in part destroyed by it, and with the base of the skull. It consisted predominantly of interlacing bundles of fusiform cells. In some places the cells were uniform in appearance while in other places there were foci of pleomorphism, where among the fusiform cells, giant mononucleated cells of various sizes with large hyperchromatic nuclei were found. This tumor, with a large number
of mitotic figures (Fig. 8), destroyed the adjacent brain tissue invaded and completely replaced the bone marrow of the neighboring part of the skull. It was either a fibrosarcoma or a malignant neurofibroma. The distinction between the two is often difficult. Its high malignancy and the absence of such microscopic features as nuclear palisading, short spindle cells in whorls, epithelioid cells with ample eosinophilic cytoplasm, etc. is in favor of the first possibility, namely that it was a fibrosarcoma. Tumor 4, in a female of the T. M. strain maintained on Purina chow supplemented with lecithin and cholesterol, had macroscopically the appearance of a brain nerve cell tumor, at the most anterior end of the frontal lobe of the left hemisphere. Upon microscopic examination it was found that medially to the above tumor there was a mass of cells of various kinds: polymorphonuclear, plasma cells, and large, more primitive histiocyte-like cells. The latter formed masses or cords; many were in mitosis; and some were binucleated (Figs. 9 and 10). The differential diagnosis lies between an unusual inflamatory process and a lympho-proliferative phenomenon. The presence of polymorphs was in favor of the first hypothesis, while the large reticuloendothelial cells were suggestive of a lymph-proliferative process.
DISCUSSION Mice maintained on a diet supplemented with egg yolk or with egg lipids develop a high incidence of lung tumors, lymphosarcoma and m a m m a r y cancer [4], while those fed vegetable fat have only a high incidence of lung neoplasms. The present results indicate that both, egg fat and vegetable oil, affect the nervous system. In a previous report it was shown that mice of the T. M. strain maintained on Purina chow supplemented with various vegetable lipids develop a relatively high incidence of nerve cell tumors of the frontal lobe [3]. The highest incidence of these tumors was found in the mice receiving lecithin and cholesterol. Contrary to a previous statement (that there are no mitotic figures in these tumors [3]), it was found recently, in tumors embedded in plastic and sectioned at one micron, that, among the completely differentiated nerve cells, there are many cells in mitosis (Fig. 11). This indicates that these are actively growing neoplasms and not masses of cells which, at an early stage, underwent proliferation, then secondarily differentiated and remained inactive.
mouse, maintained on Purina chom suf$emented with egg yolk. 619 Fig. 1. Brain of a BALBIc days old. x 3. A nodule projecting from the right hemisphere into the interhemispheric fissure is delimited laterally by a depressed area which is the place of origin of the oligodendroglioma shown in Fig. 2.
Horizontal section of the hemisphere of Fig. 1, passing through the nodule (to the left) Fig. 2. the depessed area, (in the middle) and the remaining part of the cortex to the right. Hematoxylin and eosin, X 100.
Fig.
3.
Fig. 4.
Section through the inferior and posterior end of the hemisphere and of the tumor qf Fig. 1. Hemstoxylin and eosin,
(in the right x 100.
A higher magnijcation of the tumor of Fig. 3. x 320. The tumor consists dark nuclei and clear cytoplasm. Many cells are in mitosis.
upper corner)
of cellswith
large
(to face
p. 530)
Fig. 5. Brain of a BALBIc mouse, 429 days old, maintained on Purina chow supplemented with egg yolk. x 1.5. The depressed area on the right hemisphere and the whitish nodule at its postero-superior border correspond to the place of origin of the oligodendroglioma shown in the following figure.
Fig. 6. Section passing through the whitish nodule of Fig. 5. Hematoxylin and eosin x 320. The oligodendroglioma, like in Fig. 4, consists of cells with large dark nuclei and clear cytoplasm. Many cells are in mitosis and some of the mitotic figures are abnormal.
Fig. 7. Interior surface of the brain of a mouse of the T.M. strain maintained on Purina chow supplemented with monoolein and cholesterol. x 2. Left hemisphere is compressed (below) by a large tumor situated on the trajectory of trigeminal nerve. The tumor is continuous toith the brain stem.
Fig. 8. Section of the tumor of Fig. 7. Hematoxylin andeosin. x 320. The tumor consists of bundles of fibroblasts running in all directions. A mitotic fisure is seen slightb to the right of the middle.
Fig. 9. Section of the anterior end of the hemisphere of a mouse of the T. M. strain, 700 days old, maintained on Purina chow supplemented with lecithin and cholesterol. Hematoxylin and eosin. x 100. To the right of the brain-nerve cell tumor is a mass of cells which invaginates in part between the latter and the normal cortex, which is below.
Fig.
10.
The mass of cells of Fig. 9 at higher magnification. x 320. The cells are polymorphonuclear and histiocytes. Many of the latter are in mitosis and some are binucleated.
Fig. 11. Section of a brain-nerve cell tumor of a mouse, of the T, M. strain, 5 18 days old, maintained on Purina chow supplemented with monoolein and cholesterol. Arur B and Methylene blue. x 750. It shows cross-sections of nerve fibers, a feu, di$rentiated nerve cells and a cell in mitosis, in metaphase.
Intracranial Tumors in Mice of Two Different Strains Maintained on Fat Enriched Diets
The present results demonstrate that the supporting elements of the nervous tissue may also undergo abnormal growth under the effect of a fat enriched diet. It is true that the number of tumors in this case was very small (only two of a total of 237 BALB/c mice on the diet supplemented with egg yolk developed oligodendrogliomas, one of 64 mice of the T. M. strain receiving monoolein and cholesterol developed an intracranial fibrosarcoma, and one of 88 mice on the diet supplemented with lecithin and cholesterol developed what was probably an intracranial lymphoma), but it is significant since none of the 197 BALB/c and of over 200 T. M. control mice developed such tumors. Moreover, if to the above 4 intracranial tumors are added the 37 brain nerve cell tumors, found in the mice on the diets supplemented with monoolein and cholesterol, and with lecithin and cholesterol [3], the incidence of the total number of intracranial neoplasms becomes highly significant. As for the mechanism by which a fat enriched diet affects tumorigenesis in general and that of the nervous system in particular, it is still hard to understand. W h a t seems to be striking is that cholesterol-enriched diets are particularly active. The incidence of brain-nerve cell tumors is higher in mice on a diet supplemented with glycerides and cholesterol than in those receiving glycerides alone. Cholesterol seems to affect also the pituitary gland. O f 117 mice of the T. M. strain maintained on Purina chow supplemented with refined corn oil and cholesterol, 15 developed pituitary tumors, while of 174 mice on a diet supplemented with corn oil alone only 3 developed such tumors (unpublished). It was previously reported that mice of the C57 B1 strain maintained on a diet supplemented with egg yolk (which is rich in cholesterol) had an incidence of 12% of pituitary tumors [6]. The question that could be raised is whether there is any relationship between the pituitary and the brain tumorigenesis. From the results so far obtained, it is still hard to draw any conclusion on the subject.
The mice with the intracranial tumors were offspring of mice maintained on the same diets; the question is consequently raised whether the lipids affected the animals already in utero, during the period of lactation, or during adult life. It is known that some chemical carcinogens have a transplacental effect. Druckrey and his co-workers found that following the injection of small, otherwise subthreshold doses of ethylnitroso-urea to pregnant rats practically all the offspring die of malignant tumors of the central or peripheral nervous system [7]. It has also been demonstrated that the aliphatic nitrosamines pass to the offspring of hamsters by way of the mother's milk [5]. The natural carcinogen cycasin and its Aglycon reach the offspring by way of the placenta and by the mother's milk [8]. According to Druckrey and his co-workers, during fetal development the sensitivity to the carcinogen is at least ten-fold higher than during the adult life of the animal, which could be attributed to the greater activity of the nucleic acids--the target of the primary carcinogenic action [7]. As for the fat enriched diets there is no indication that the lipids affect the nervous system of the offspring in utero. In no case did all the offspring of one litter die at an early age of tumors of the nervous system (brain nerve cell tumors and neoplasia of the supporting elements). Offspring of mice, on the fat enriched diets, foster nursed by control mice have, like the latter, a low incidence of tumors. There is some indication that the fat enriched diets affect the endocrine system during the period of lactation. In previous experiments it was found that a few of the mice, removed from the fat enriched diets immediately after weaning, developed pituitary tumors at the age of over 2 years. The problem is still being studied.
Acknowledgement--Some of the slides were examined by Dr. L.J. Rubinstein, Professor of Neuropathology at Stanford University School of Medicine, to whom I am greatly indebted.
REFERENCES 1. 2. 3. 4.
531
C. HOCH-LIGETIand D. S. RUSSELL,Primary tumors of the brain and meninges in rats fed 2-acetylaminofluorene. Acta Un. Int. Cancr. 7, 126 (1950). G. STOOBRANDTand J. M. BRUCHER,Etudes de tumeurs nerveuses obtenues par l'administration de m~thylnitrosour~e au rat. Neuro-chirurgie 14, 515 (1968). J. SZEPSENWOL,Brain nerve cell tumors in mice on diets supplemented with various lipids. Path. Microb. 34, (1969). J. SZEPSENWOL, Carcinogenic effect of ether extract of whole egg, alcohol extract of egg yolk and powdered egg free of the ether extractable part in mice. Proc. Soc. exp. biol. Med. 116) 1136 (1964).
532
J. Szepsenwol
5. 6. 7. 8.
U. MOHR and J. ALTHOFF,Carcinogenic activity of aliphatic nitrosamines via the mother's milk in the offspring of Syrian golden hamsters. Proc. Soc. exp. biol. Med. 136, 1007 (1971). J. SZEPSENWOL,Carcinogenic effect of egg yolk in mice of the C57 B1 strain. Proc. Soc. exp. biol. Med. 122~ 981 (1966). H. DRUCKREY,R. PREUSSMANN,S. IVANKOVICand D. SCnMAHL, Organotrope carcinogene Wirkungen bei N-Nitroso-Verbindungen an BD-Ratten. Z. Krebsforsch. 69~ 103 ( 1967). M. SPATZand G. L. LA•UEUR, Evidence for transplacental passage of the natural carcinogen cyeasin and its aglycone. Proc. Soc. exp. biol. Med. 127, 281 (1968).
Intracranial Tumors in Mice of Two Different Strains Maintained on Fat Enriched Diets* J. SZEPSENWOL Department of Anatomy, University of P. R. School of Medicine, San Juan, Puerto Rico A b s t r a c t - - T w o mice of BALB/c strain maintained on Purina chow supplemented with egg yolk developed, one at the age of 619 days and the other one at the age of 429 days, oligodendrogliomas originating from the cortex of the right hemisphere. The tumor of the first mouse invaded the interhemisphericfissure and extended to the brain stem and the posterior pole of the hemisphere. Two other mice of the T. M. strain, maintained on Purina chow supplemented with monoolein and cholesterol, and with lecithin and cholesterol, developedat the ages of 804 and 700 days respectively a fibrosarcoma associated with trigeminal nerve in the first case, and a brain-nerve cell tumor of the left hemisphere complicated by what appears to be a lymphoma in the second case. None of the control mice of the two strains developedintracranial tumors.
INTRODUCTION
strain, maintained on Purina chow supplemented with raw egg yolk, and the other two in mice of the T. M. strain maintained on Purina chow supplemented with vegetable lipids.
NEOPLASMS of the nervous system have been induced in mice and rats by direct application of carcinogenic hydrocarbons such as benzpyrene, dibenzanthracene, dimethylbenzanthracene and methylcholanthrene. T h e y have also been obtained by administration, via the digestive tube, of 2-acetylaminofluorene [1]. More recently, various nitrosamine compounds, administered either intravenously of per os, were found to induce in rodents tumors of the central and peripheral nervous systems [2]. O n the other hand, it was found that mice maintained on Purina chow supplemented with various lipids develop tumors of the cerebral cortex consisting entirely of differentiated nerve cells [3]. The present study is a report of 4 intracranial tumors, of a different nature, found in mice of two different strains maintained, as the above mentioned mice, on fat enriched diets. T w o of these tumors were in mice of the BALB/c
MATERIAL AND METHODS
The BALB/c mice? have been maintained on Purina chow supplemented with raw egg yolk (one egg yolk per 25-30 mice daily), while for the mice of the T. M. strain, like in previous experiments [3], the Purina chow was supplemented with small amounts of vegetable oil. In both cases, the mice were placed on the above diets at the age of 4 weeks, they were bred and their offspring maintained on the same diets. Mice of both strains maintained on Purina chow only, without supplements, were used as controls. The mice were killed when they were rapidly loosing weight. The skull was opened and the brain carefully examined. Those with tumors were fixed with Bouin's fluid, or with a 10% solution of formaldehyde, embedded in paraffin, sectioned serially and stained with hematoxylin and eosin. In some cases other staining techniques were used.
Accepted 21 May 1971. * Supported by General Research Grant FR 5419-04. t The original BALB/c mice were supplied by H. B. Andervont. Nat. Cancer Inst. Bethesda, MD. to whom we are greatly indebted. 529
530
J. Szepsenwol RESULTS
The two BALB/c mice with brain tumors (tumors 1 and 2) were both males; one was 619 and the other 429 days old. They were both on the Purina chow supplemented with egg yolk from the day they were born: they were offspring of mice maintained on the same diet. Macroscopically, the brain of the mouse 619 days old had a nodule projecting from the right hemisphere into the interhemispheric fissure and delimited laterally by a depressed area (Fig. 1). This nodule, as seen in sections, was actually not the tumor; it consisted of normal hemispheric tissue. It was separated from the rest of the cortex by a growing mass of cells extending from the depressed area of the hemisphere (Fig. 2) along the interhemispheric fissure to the brain stem and the inferior surface of the hemisphere (Fig. 3), and having all the characteristics of an oligodendroglioma. It was cellular and the cells had relatively large dark nuclei and clear cytoplasm. M a n y of them were in mitosis and some of the mitotic figures were abnormal (Fig. 4). The second BALB/c mouse, 429 days old, presented a large depressed area on the lateral surface of the right hemisphere with a small whitish nodule emerging from its posterosuperior end (Fig. 5). In microscopic sections this part of the hemisphere consisted, like tumor i, of a mass of cells with large dark nuclei and clear cytoplasm (Fig. 6). Mitotic figures, some of which were abnormal, were abundant. This, as in the previous case, was without any doubt an oligodendroglioma. O f the two intracranial tumors (tumors 3 and 4) in mice of the T. M. strain one was in a female 804 days old (maintained on Purina chow supplemented with monoolein and cholesterol) and the other one in a female 700 days old (maintained on Purina chow supplemented with lecithin and cholesterol). They were both offspring of mice maintained on the same diets. T u m o r 3, in the mouse on the diet supplemented with monoolein and cholesterol, appeared as a large mass on the trajectory of the left trigeminal nerve (Fig. 7). It was continuous with the brain stem, with the lateral surface of the hemisphere, which was compressed and in part destroyed by it, and with the base of the skull. It consisted predominantly of interlacing bundles of fusiform cells. In some places the cells were uniform in appearance while in other places there were foci of pleomorphism, where among the fusiform cells, giant mononucleated cells of various sizes with large hyperchromatic nuclei were found. This tumor, with a large number
of mitotic figures (Fig. 8), destroyed the adjacent brain tissue invaded and completely replaced the bone marrow of the neighboring part of the skull. It was either a fibrosarcoma or a malignant neurofibroma. The distinction between the two is often difficult. Its high malignancy and the absence of such microscopic features as nuclear palisading, short spindle cells in whorls, epithelioid cells with ample eosinophilic cytoplasm, etc. is in favor of the first possibility, namely that it was a fibrosarcoma. Tumor 4, in a female of the T. M. strain maintained on Purina chow supplemented with lecithin and cholesterol, had macroscopically the appearance of a brain nerve cell tumor, at the most anterior end of the frontal lobe of the left hemisphere. Upon microscopic examination it was found that medially to the above tumor there was a mass of cells of various kinds: polymorphonuclear, plasma cells, and large, more primitive histiocyte-like cells. The latter formed masses or cords; many were in mitosis; and some were binucleated (Figs. 9 and 10). The differential diagnosis lies between an unusual inflamatory process and a lympho-proliferative phenomenon. The presence of polymorphs was in favor of the first hypothesis, while the large reticuloendothelial cells were suggestive of a lymph-proliferative process.
DISCUSSION Mice maintained on a diet supplemented with egg yolk or with egg lipids develop a high incidence of lung tumors, lymphosarcoma and m a m m a r y cancer [4], while those fed vegetable fat have only a high incidence of lung neoplasms. The present results indicate that both, egg fat and vegetable oil, affect the nervous system. In a previous report it was shown that mice of the T. M. strain maintained on Purina chow supplemented with various vegetable lipids develop a relatively high incidence of nerve cell tumors of the frontal lobe [3]. The highest incidence of these tumors was found in the mice receiving lecithin and cholesterol. Contrary to a previous statement (that there are no mitotic figures in these tumors [3]), it was found recently, in tumors embedded in plastic and sectioned at one micron, that, among the completely differentiated nerve cells, there are many cells in mitosis (Fig. 11). This indicates that these are actively growing neoplasms and not masses of cells which, at an early stage, underwent proliferation, then secondarily differentiated and remained inactive.
mouse, maintained on Purina chom suf$emented with egg yolk. 619 Fig. 1. Brain of a BALBIc days old. x 3. A nodule projecting from the right hemisphere into the interhemispheric fissure is delimited laterally by a depressed area which is the place of origin of the oligodendroglioma shown in Fig. 2.
Horizontal section of the hemisphere of Fig. 1, passing through the nodule (to the left) Fig. 2. the depessed area, (in the middle) and the remaining part of the cortex to the right. Hematoxylin and eosin, X 100.
Fig.
3.
Fig. 4.
Section through the inferior and posterior end of the hemisphere and of the tumor qf Fig. 1. Hemstoxylin and eosin,
(in the right x 100.
A higher magnijcation of the tumor of Fig. 3. x 320. The tumor consists dark nuclei and clear cytoplasm. Many cells are in mitosis.
upper corner)
of cellswith
large
(to face
p. 530)
Fig. 5. Brain of a BALBIc mouse, 429 days old, maintained on Purina chow supplemented with egg yolk. x 1.5. The depressed area on the right hemisphere and the whitish nodule at its postero-superior border correspond to the place of origin of the oligodendroglioma shown in the following figure.
Fig. 6. Section passing through the whitish nodule of Fig. 5. Hematoxylin and eosin x 320. The oligodendroglioma, like in Fig. 4, consists of cells with large dark nuclei and clear cytoplasm. Many cells are in mitosis and some of the mitotic figures are abnormal.
Fig. 7. Interior surface of the brain of a mouse of the T.M. strain maintained on Purina chow supplemented with monoolein and cholesterol. x 2. Left hemisphere is compressed (below) by a large tumor situated on the trajectory of trigeminal nerve. The tumor is continuous toith the brain stem.
Fig. 8. Section of the tumor of Fig. 7. Hematoxylin andeosin. x 320. The tumor consists of bundles of fibroblasts running in all directions. A mitotic fisure is seen slightb to the right of the middle.
Fig. 9. Section of the anterior end of the hemisphere of a mouse of the T. M. strain, 700 days old, maintained on Purina chow supplemented with lecithin and cholesterol. Hematoxylin and eosin. x 100. To the right of the brain-nerve cell tumor is a mass of cells which invaginates in part between the latter and the normal cortex, which is below.
Fig.
10.
The mass of cells of Fig. 9 at higher magnification. x 320. The cells are polymorphonuclear and histiocytes. Many of the latter are in mitosis and some are binucleated.
Fig. 11. Section of a brain-nerve cell tumor of a mouse, of the T, M. strain, 5 18 days old, maintained on Purina chow supplemented with monoolein and cholesterol. Arur B and Methylene blue. x 750. It shows cross-sections of nerve fibers, a feu, di$rentiated nerve cells and a cell in mitosis, in metaphase.
Intracranial Tumors in Mice of Two Different Strains Maintained on Fat Enriched Diets
The present results demonstrate that the supporting elements of the nervous tissue may also undergo abnormal growth under the effect of a fat enriched diet. It is true that the number of tumors in this case was very small (only two of a total of 237 BALB/c mice on the diet supplemented with egg yolk developed oligodendrogliomas, one of 64 mice of the T. M. strain receiving monoolein and cholesterol developed an intracranial fibrosarcoma, and one of 88 mice on the diet supplemented with lecithin and cholesterol developed what was probably an intracranial lymphoma), but it is significant since none of the 197 BALB/c and of over 200 T. M. control mice developed such tumors. Moreover, if to the above 4 intracranial tumors are added the 37 brain nerve cell tumors, found in the mice on the diets supplemented with monoolein and cholesterol, and with lecithin and cholesterol [3], the incidence of the total number of intracranial neoplasms becomes highly significant. As for the mechanism by which a fat enriched diet affects tumorigenesis in general and that of the nervous system in particular, it is still hard to understand. W h a t seems to be striking is that cholesterol-enriched diets are particularly active. The incidence of brain-nerve cell tumors is higher in mice on a diet supplemented with glycerides and cholesterol than in those receiving glycerides alone. Cholesterol seems to affect also the pituitary gland. O f 117 mice of the T. M. strain maintained on Purina chow supplemented with refined corn oil and cholesterol, 15 developed pituitary tumors, while of 174 mice on a diet supplemented with corn oil alone only 3 developed such tumors (unpublished). It was previously reported that mice of the C57 B1 strain maintained on a diet supplemented with egg yolk (which is rich in cholesterol) had an incidence of 12% of pituitary tumors [6]. The question that could be raised is whether there is any relationship between the pituitary and the brain tumorigenesis. From the results so far obtained, it is still hard to draw any conclusion on the subject.
The mice with the intracranial tumors were offspring of mice maintained on the same diets; the question is consequently raised whether the lipids affected the animals already in utero, during the period of lactation, or during adult life. It is known that some chemical carcinogens have a transplacental effect. Druckrey and his co-workers found that following the injection of small, otherwise subthreshold doses of ethylnitroso-urea to pregnant rats practically all the offspring die of malignant tumors of the central or peripheral nervous system [7]. It has also been demonstrated that the aliphatic nitrosamines pass to the offspring of hamsters by way of the mother's milk [5]. The natural carcinogen cycasin and its Aglycon reach the offspring by way of the placenta and by the mother's milk [8]. According to Druckrey and his co-workers, during fetal development the sensitivity to the carcinogen is at least ten-fold higher than during the adult life of the animal, which could be attributed to the greater activity of the nucleic acids--the target of the primary carcinogenic action [7]. As for the fat enriched diets there is no indication that the lipids affect the nervous system of the offspring in utero. In no case did all the offspring of one litter die at an early age of tumors of the nervous system (brain nerve cell tumors and neoplasia of the supporting elements). Offspring of mice, on the fat enriched diets, foster nursed by control mice have, like the latter, a low incidence of tumors. There is some indication that the fat enriched diets affect the endocrine system during the period of lactation. In previous experiments it was found that a few of the mice, removed from the fat enriched diets immediately after weaning, developed pituitary tumors at the age of over 2 years. The problem is still being studied.
Acknowledgement--Some of the slides were examined by Dr. L.J. Rubinstein, Professor of Neuropathology at Stanford University School of Medicine, to whom I am greatly indebted.
REFERENCES 1. 2. 3. 4.
531
C. HOCH-LIGETIand D. S. RUSSELL,Primary tumors of the brain and meninges in rats fed 2-acetylaminofluorene. Acta Un. Int. Cancr. 7, 126 (1950). G. STOOBRANDTand J. M. BRUCHER,Etudes de tumeurs nerveuses obtenues par l'administration de m~thylnitrosour~e au rat. Neuro-chirurgie 14, 515 (1968). J. SZEPSENWOL,Brain nerve cell tumors in mice on diets supplemented with various lipids. Path. Microb. 34, (1969). J. SZEPSENWOL, Carcinogenic effect of ether extract of whole egg, alcohol extract of egg yolk and powdered egg free of the ether extractable part in mice. Proc. Soc. exp. biol. Med. 116) 1136 (1964).
532
J. Szepsenwol
5. 6. 7. 8.
U. MOHR and J. ALTHOFF,Carcinogenic activity of aliphatic nitrosamines via the mother's milk in the offspring of Syrian golden hamsters. Proc. Soc. exp. biol. Med. 136, 1007 (1971). J. SZEPSENWOL,Carcinogenic effect of egg yolk in mice of the C57 B1 strain. Proc. Soc. exp. biol. Med. 122~ 981 (1966). H. DRUCKREY,R. PREUSSMANN,S. IVANKOVICand D. SCnMAHL, Organotrope carcinogene Wirkungen bei N-Nitroso-Verbindungen an BD-Ratten. Z. Krebsforsch. 69~ 103 ( 1967). M. SPATZand G. L. LA•UEUR, Evidence for transplacental passage of the natural carcinogen cyeasin and its aglycone. Proc. Soc. exp. biol. Med. 127, 281 (1968).