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The toxicity of purified cellulose in studies with laboratory animals
Cancer Letters, 63 (1992) 83-92 Elsevier Scientific Publishers Ireland
a3 Ltd.
Review Letter
The toxicity animals R.L.
Andersona,
“1004A Celestial, 45224-1788
of purified
J.W.
Cincinnati,
(USA)
and
Owensb OH 45202,
‘Procter
&
and ‘Procter Gamble
cellulose
C.W.
in
studies
with
laboratory
Timmsc
& Gamble Paoer Products, Strasse GmbH, Sulbzocher
6200
Center
40,
D-6231
Hi/f Road, Cincinnati, Schwalbach
am
OH
Taunus
(Germany) (Received 13 October 1991) (Revision received 27 January (Accepted 28 January 1992)
1992)
Summary
Introduction
The available literature has been reviewed for studies in laboratory animals using purified of purified cellulose, as the production cellulose may result in trace organochlorine The chronic ingestion of contamination. purified cellulose over the entire lifespans in rats and mice does not result in any increase in spontaneous disease or neoplasia. Further, purified cellulose does nor display promotional activity in the mammary gland, the colon, or the bladder of rats and does not significantly alter the absorption or the metabolism of dietary components. No adverse effects were found on reproduction or neonate development in rats and mice. Therefore, no adverse health effects in humans are expected from exposure to purified cellulose.
The industrial production of cellulose is based on the removal of lignin and hemicellulose from wood to yield a purified cellulose for use in a wide array of products. Historically, molecular chlorine has been used lignin, resulting in to remove trace organochlorine residuals in the fiber. Measured as elemental chlorine, water and organic solvents extract an average of 250 ppm chlorine from softwood fiber [1,2]. Risk assessments have been performed only for individual compounds such as 2,3,7,8tetrachloro-dibenzo-p-dioxin (TCDD) [3,4]. Further, no comprehensive review of cellulose safety has occurred since 1972 when purified cellulose was declared to be generally recognized as safe (GRAS) by the United States Food and Drug Administration based upon a review of research between 1920 and 1972 [5]. For purified cellulose, the primary public health concern is carcinogenesis, focusing on the organochlorine residuals which include TCDD, a well-known carcinogen (6 and Refs.
Keywords: cellulose; ganochlorines;
diet; neoplasia; reproduction; promotion
Correspondence to: J.W. Owens, Procter Products, 6100 Center Hill Road, Cincinnati,
or-
& Gamble Paper OH 45224-1788,
USA.
0304-3835/92/$05.00 Printed and Published
0 1992 Elsevier Scientific Publishers in Ireland
Ireland
Ltd
84
therein). This review searched for animal studies from the published literature where industrially purified cellulose has been added to the diet as either an inert ingredient or as a diluent. These studies are appropriate for a safety evaluation since many of the chlorinated impurities in purified cellulose have not been identified and valid bioassays do not exist for the identified compounds. Therefore, the actual complex mixture of residuals is evaluated rather than estimating the interaction of individual, identified compounds. For clarity, this material is described as exogenous cellulose to distinguish it from natural plant or endogenous cellulose present in cereals included in chow diets. Oral administration studies using exogenous, purified cellulose were found to assess: (1) alteration of tumor expression in animal models (promotion), (2) responses in chronic, lifetime ingestion studies while monitoring spontaneous disease and neoplasms in both rats and mice and (3) reproduction and neonate development. These chronic studies either directly included chow based diets or chow based studies were available for comparison using the same animal strains. Therefore, a weight of the evidence review of this published literature was undertaken. The literature was also reviewed for other mechanisms which could influence chronic studies: (1) inhibition of digestive enzymes, (2) the metabolism of dietary components and (3) the morphology and structure of the gastrointestinal (GI) tract. Chronic
exposure
studies
with
exogenous
cellulose
The 1972 a GRAS document reviewed chronic cellulose feeding studies and concluded that there were no indications for adverse effects on human health. However, the longest laboratory animal feeding study available was 18 months. No recent studies were found specifically testing the effect of chronic exogenous cellulose ingestion on spontaneous disease development in laboratory animals. Studies of a purified cellulose derivative,
methylcellulose, were found using Sprague Dawley rats in a 2-year feeding study at 0%) 1% and 5% concentrations. The results indicated no evidence for differences in spontaneous disease rates or neoplasia from the ingestion of this cellulose derivative [7]. The largest study utilizing exogenous cellulose was by Maurer et al. [8] who conducted a bioassay of dietary sodium fluoride. Two diets were used: Purina Chow and a 5% exogenous cellulose-containing semipurified diet with a control group and three sodium fluoride groups. The study employed groups of 20 rats of each sex per treatment for interim sacrifices and 50 rats of each sex per treatment designated for the chronic exposure so that the a total of 400 animals received the exogenous cellulose diet in chronic exposures. Survival of the females but not the males was greater on the Purina Chow. Comparing Purina Chow to the 5% exogenous cellulose-containing diets, gross and histological evaluations indicated that exogenous cellulose was not associated with any increase in the incidence or severity of either non-neoplastic or neoplastic lesions. Spontaneous renal mineralization and an increased incidence of hepatocyte vacuolar changes were the result of high caloric intake and rapid growth and not a function of cellulose ingestion per se. Caloric restriction with constant cellulose ingestion prevents the expression of both of these lesions [9] (see Tables 1 and 2). In a second study, Anastasia et al. [lo] compared a Purina Chow to two semi-purified diets containing 3% purified cellulose (Celluflour) ( - 1.2 g cellulose/kg body wt. per day). The diets were fed ad libitum to groups of 50 rats per sex with scheduled sacrifices at 3, 6, 12 and 22 months. The semi-purified diets resulted in greater total weight gain with lower relative organ weights (g/100 g body wt.) as absolute organ weights were higher in cellulose-fed groups. Histopathology differences were limited to enhanced kidney mineralization in semi-purified diet females and to diffuse perinuclear hepatocyte vacuolization in the semi-purified diet males.
85 Table 1. Effect of caloric restriction on chronic nephropathy in male rats ingesting diets containing purified cellulose. Nephropathy grade ’
% Incidence Ad libitum
0 1 2 3 4 E
(1211
Restricted (106)
4 8 15 20 21 32
16 66 13 3 0 2
The study employed male, containing 3% exogenous or restricted to 60% of the group. Values for animals dying spontaneously. Data ‘Higher numbers indicate stage. Values in parantheses
Fisher 344 rats ingesting a diet cellulose fed either ad libitum caloric intake of the ad libitum killed at interim sacrifices and derived from Maeda et al. [9]. more severe lesions. E, endrepresent number of animals.
Both of these findings were previously reported in rats ingesting semi-purified diets and were not considered significantly related to exogenous cellulose consumption [ 111. The percentage incidence of neoplasms and
Table 2. Effect of caloric restriction on fatty changes in the liver of rats ingesting diets containing purified cellulose. Fatty change grade ’
0 1 2 3
% Incidence Ad libitum
Restricted
(121)
(106)
27 45 21 7
66 25 9 0
Results include animals from scheduled sacrifices and dying spontaneously. Values in parentheses represent number of animals. See Table 1 for dietary details. Data derived from Maeda et al. [9]. ‘Higher numbers indicate more severe lesions.
specific neoplasm types did not differ significantly between the chow diet and either of the cellulose-containing diets. The authors concluded that the semi-purified diets containing exogenous cellulose did not significantly alter the health of the rats. Caloric
restriction
studies
Exogenous cellulose has been a dietary component in chronic feeding studies evaluating spontaneous disease and neoplasia during lifetime caloric restriction. Lifetime caloric restriction increases longevity and delays the expression of spontaneous disease, including an apparent increase in the latency period for neoplasia (see Ref. 12 for a review). For example, lifetime caloric restriction studies were conducted using male Fischer 344 rats ingesting a diet containing 3% exogenous cellulose (Solka Floe). These rats were maintained in a barrier restricted environment to prevent infection until either scheduled interim sacrifices or death [9]. One group consumed their diet ad libitum, while intake in another group was restricted to 60% of that of the ad libitum group as described by Yu et al. [13]. The groups consumed equivalent nutrients over their lifetime (36.3 x lo3 kcal/rat for the ad libitum vs. 35.7 x lo3 kcal/rat for the restricted group) and equivalent amounts of exogenous cellulose (- 270 g/rat). Due to the difference in body weights, the daily relative dose of cellulose was also equivalent at - 1 g/ kg body wt. per day. Caloric restriction was associated with less disease and a delay in the expression of disease at the three primary sites (kidney, liver and heart) noted in the rats fed ad libitum [9]. In terms of neoplasms, the restricted group displayed a marked delay in the appearance of neoplasms, but the total lifetime incidence of neoplasms was unchanged (Table 3). To further assess the interplay of caloric restriction and exogenous cellulose ingestion, the above described rats can be compared with rats of the same strain consuming a cerealbased diet, ad libitum for up to 33 months [14]. The principle causes of death in both
86 Table 3.
Effect of caloric restriction on the incidence of neoplasms other than testicular tumors in rats ingesting diets containing purified cellulose. Tumor classification Benign
Tumorbearing rats
Malignant % incidence
Ad Libitum (121) Restricted (106)
37
16
39
34
31
42
Sum of all tumors in animals from scheduled sacrifices and spontaneous deaths. Values in parentheses represent number of animals. See Table 1 for details. Data derived from Maeda et al. [9].
studies
advanced renal disease and Neoplasia comparisons between the rats ingesting the cereal-based diet and those ingesting the exogenous cellulosecontaining diet demonstrate a strong similarity in the time of appearance, target organ and incidence rate of neoplasms. This shows that lifetime spontaneous disease and neoplasia development are not influenced by ingesting exogenous cellulose chronically at least at a level of 3% in the diet or - 1 g/kg body wt. per day. Mice respond to dietary restriction with a similar increase in longevity and a delay in spontaneous disease [ 121. One study by Weindruch et al. [15] compared a cereal-based chow group to two groups consuming a semipurified diet containing 5.6% exogenous cellulose using females of a long-lived hybrid strain (Fr progeny from C3HSW/Sn females mated with C57BLlO.RIII/Sn males). The cellulose consuming groups were fed either 7 times per week for 15% restriction (4.6 g cellulose/kg body wt.) or 4 times per week for 50% restriction (3.1 g cellulose/kg body wt.). Mean lifespans were 27.4 months for ad libitum, chow-fed mice, 32.7 months for the cellulose-containing diet fed 7 times per week neoplasms.
were
and 42.3 months for the cellulose-containing diet fed 4 times per week. Lifetime cancer incidence was not influenced by either the caloric intake or exogenous cellulose in the diet. Although the onset of neoplasms was delayed in the caloric-restricted mice, no difference in survival rates or survival times after tumor onset occurred. Therefore, the lifetime ingestion of exogenous cellulose does not alter the incidence of spontaneous disease or neoplasms in either mice or rats, providing no evidence for carcinogenic activity. The liver is an organ of special interest as a primary site of toxicity with many halogenated organics. In this regard, the spontaneous liver pathology in male Fischer-344 rats allowed to live their maximal lifespan while ingesting either a cereal-based diet [14] or a semipurified diet containing 3% exogenous cellulose (Solka Floe) [9] can be compared. All of these animals showed similar liver pathology and the incidence of liver tumors was always less than 1% . This reinforces the evidence that exogenous cellulose and its residuals after lifetime ingestion do not display either promotional or carcinogenic activity in the liver. No studies were found in the literature directly comparing exogenous cellulose from processes with and without molecular chlorine. However, molecular chlorine bleaching of wheat flour has been tested in chronic ingestion studies in both rats 1161 and mice [17]. Bleached wheat flour containing residuals with 1250 and 3000 ppm organically-bound chlorine comprised 30% of the diet in both studies. In addition, two control diets were used in both studies: an unbleached flour containing diet and a cereal-based diet. The unbleached flour containing diet provides the higher caloric density of flour to act as a control versus the cereal-based diet. Rats were fed these diets for 104 weeks and mice for 17 months. When compared to the cerealbased diets, both higher caloric, flour-based diets decreased the survival of female rats, but not males. No differences were observed between the organochlorine containing bleached and the unbleached group in longevity,
87
spontaneous disease, or incidence of neoplasia for any tissue in either rats or mice. Exogenous cellulose and tumor models If exogenous cellulose residuals had cancer promoting activities, then the assumption is that diets containing exogenous cellulose should lead to an increased cancer rate when administered subsequent to a dose of a sitespecific carcinogen. Studies designed to determine the effect of high-fat diets on tumor promotion in the GI tract and in the breast of experimental animals have employed a broad range of dietary exogenous cellulose levels. Exogenous cellulose does not display tumor promotion activity on the colon at large doses. In rats, 10 -30% exogenous cellulose in the diet has been ingested for 24 weeks after exposure to azoxymethane (AOM) to induce large bowel tumors. Tumor rates in animals ingesting exogenous cellulose were lower comcompared to the fiber-free controls (Table 4) [18]. In a second study, rats induced with dimethylhydrazine (DMH) consumed diets containing 0% , 4.5%, or 9% exogenous cellulose. Again, the groups ingesting exogenous cellulose had a lower incidence of colon tumors than the group consuming a cellulose-free diet. Tumor rates in the small bowel also decreased, but did not attain statistical significance [ 191. Newberne and Schrager (1991) have summarized the effects of cellulose on experimentally induced colo-
Table 4. Effect of purified cellulose ingestion on the incidence of large bowel tumors in rats exposed to azoxymethane. Average tumors/rat
Diet
Fiber-free + 35% 10% Cellulose + Fiber-free + 6% 20% Cellulose + 30% Cellulose +
tallow 35% tallow tallow 6% tallow 6% tallow
8.44 7.88 4.04 2.86 1.95
Data are taken from Nigro et al. [18]
rectal tumors in rodents, noting no adverse effect in six studies and in only one study was there an enhancement [20]. Additional exogenous cellulose feeding studies have used the rat mammary gland as a carcinogenic target with similar results. Kritchevsky et al. [21] fed rats diets containing 8 - 46 % exogenous cellulose with different levels of fat for mammary tumor promotion for 120 or 134 days after exposure to dimethylbenzanthracene (DMBA). With constant caloric intake, cellulose levels (12% and 32%) in the diet fed after initiation were without effect on tumor incidence. Further, a high-fat, ad libitum diet fed with high levels of cellulose (46%) resulted in a lower tumor incidence than a low-fat diet with a low level of cellulose (8%). Finally, caloric restriction at constant mineral and cellulose ingestion rates resulted in a 0% incidence of mammary tumor compared to 58% for the non-restricted group ingesting the equivalent amounts of purified cellulose [21]. In a second study, the effect of caloric restriction was tested on mammary tumorigenesis in DMBA-exposed female rats and colon tumorigenesis in DMH-exposed male rats. The control and restricted animals consumed the same amounts of cellulose and a lower tumor incidence was observed at both sites at equivalent cellulose intake levels (Table 5) [22]. In a third study, the effect of caloric intake on DMBA tumorigenesis in female F344 rats was studied using diets containing 5% cellulose with 5% and 30% corn oil. The mammary tumor incidences on these diets were 75%) 8% and 42 % at cellulose intakes of 2.2 g/kg (30% corn oil, ad libitum) , 2.1 g/kg (30% corn oil, restricted) and 3.4 g/ kg (5% corn oil ad libitum) , respectively [23]. Thus, in no case was mammary tumorigenesis proportional to cellulose ingestion, but was highly correlated only with caloric intake. In addition, the bladder was the target for promotional studies of sodium ascorbate and sodium saccharinate in conjunction with exogenous cellulose diets. Tumorigenesis was reduced when these salts were fed in a semipurified diet (AIN-76) containing 5%
88 Table 5. cellulose.
Effect of caloric restriction
on mammary
Ad libitum DMBA induced mammary Tumor incidence (%) Total tumor yield (W) Mean tumor weight (g)
tumors 80 64 2.8
DMH induced colon tumors Tumor incidence (46) Total tumor yield (W) Data are taken from Kritchevsky
l
1.1
100 63
and colon tumorigenesis
Restricted
Statistic
20 4 0.2*0.1
P < 0.001 P c 0.001 P < 0.01
53 20
P < 0.001 P < 0.001
purified
et al. [21].
exogenous cellulose versus a Purina Chow diet [24]. Therefore, the available evidence suggests that exogenous cellulose residuals do not display tumor promoting activity in the mammary gland, the colon, or the bladder, when administered at high oral doses. Cellulose
in rats ingesting diets containing
effects on reproduction
and growth
The GRAS report concluded that exogenous cellulose did not induce adverse reproductive effects, based on a three generation reproductive study in rats using purified cellulose at a 30% level in the diet [5]. In subsequent studies, reproduction in both rats and mice has been compared in animals ingesting an open formula, cereal-based diet (NIH-07) and a semi-purified diet (AIN-76) containing 5% exogenous cellulose [25]. In rats bred twice and mice bred continuously, reproductive performance was comparable in terms of pups per litter, pup survival and pup growth. Teratogenic effects were not observed and growth rates in both species for up to 18 weeks after weaning were unaffected. Thus, 5% exogenous cellulose ingestion did not adversely influence either reproduction or growth and development in rats or mice. In additional growth studies, dietary levels of exogenous cellulose up to 20% by weight did not retard growth in adult rats [26,27]. In rat
pups, the effects of exogenous cellulose (Avicel-PH) at 0%, 58, 10% and 20% in the diet were studied on carcass composition in rat pups after 28 days of ad libitum ingestion. The pups ingesting the 10 and 20% cellulose diets did not increase food consumption to compensate for the caloric dilution and gained less weight [28]. In a second study, 4.8%) 9.1%) 16.7% and 28.6% exogenous cellulose was added to the diet for 4 weeks and crude protein quality was varied. At the highest dose, the cellulose containing diet did decrease carcass fat due to lower caloric intake, but all other differences were dependent upon protein quality and not the cellulose content [29]. High-calorie, high-quality protein components can compensate for caloric dilution to confirm the lack of toxicity with exogenous cellulose. Feeding 40% levels of exogenous cellulose in isocaloric, isonitrogenous diets did not effect growth when compared to a diet with 5% cellulose [30]. The growth of rat pups was only slightly decreased by ingestion of a low-carbohydrate diet containing 41% cellulose (Solka Floe) introduced at parturition to their dams and then to the pups for 10 weeks after weaning [31]. Therefore, ingestion of massive cellulose doses has no apparent adverse effect on pup growth and development in either mice or rats.
89
Exogenous
cellulose and dietary component
metabolism
Any substantive differences in nutrient metabolism might confound the interpretation of exogenous cellulose safety, especially during chronic feeding studies. Cellulose does not substantially alter the fate of glucose [32], stool lipid and stool nitrogen [33], or serum cholesterol levels 1341 in humans. Although mineral balance is potentially influenced by metal ion chelation with hydroxyl and carboxyl groups in cellulose, no detrimental effects have been observed in rats (see Table 6) [27,35,36]. Exogenous cellulose and GI tract effects As the GI tract is directly exposed to ingested cellulose and any trace residuals, the effects on intestinal structure and physiology are important endpoints for the safety evaluation
Table 6. Mineral excretion cellulose (5% C) r. Element
Diet
in young and old rats ingesting either a fiber-free
% of ingested
minerals
Urine
P Mg Fe cu Zn Mn
FF 5% c FF 5% c FF 5% c FF 5%C FF 5% c FF 5% c FF 5% c
1.3 0.8 26 19 19 15 -
6*1 4*1 0.7 f 0.2 0.5 f 0.1 < 0.1 < 0.1
5% purified
Old rats Feces
f 0.3 zt 0.3 zt 5 ztz 2 f 4 f 5
(FF) diet OT a diet containing
excreted
Young rats
Ca
of exogenous cellulose. The available data show that large doses of exogenous cellulose ingested for extended periods do not adversely alter cell morphology or cell dynamics in the GI tracts of experimental animals. In rats, a diet containing 15% exogenous cellulose (Solka Floe) did not alter the morphology of the small or large intestine compared to groups ingesting a cereal-based diet [37]. A diet containing 10% cellulose (Avicel PH-105) was compared to a fiber-free diet in rats after 35 weeks of ingestion. The exogenous cellulose did not influence body weight gain, cecal surface area or colon length, or epithelial cell cycle distribution from the proximal or distal colon. The latter finding indicated that exogenous cellulose did not alter colon cell turnover or proliferation [38]. In mice, no differences in the structure and the histology of the intestine were found between the group ingesting 30% exogenous
73 59 39 35 47 35 93 66 84 70 103 86 115 96
Urine zt 8 f 4 l 3 f 2 f 5 f 2 zt 10 l 4 f 11 f 4 f 10 l 5 l 11 f 5
2.4 * 2.1 f 28 * 22 f 21 f 20 f 8&l 7*1 1.3 f 1.0 f 0.3 * 0.2 f
Feces 0.3 0.2 2 2 2 2
0.2 0.1 0.06 0.04
103 93 58 57 63 46 93 87 66 61 96 86 104 92
l 5 zt 4 + 3 f 2 ziz 3 f 2 ziz 4 ztz 4 f 4 zt 3 f 5 f 3 f 5 zt 4
The study employed male, Fischer 344 rats ingesting a purified diet (AIN-76A) containing either no fiber or 5% cellulose. The young rats were -3 weeks past weaning (data are from Wood and Stall 1361) and the old rats were 21 months old (Wood, unpublished data). ‘Each value is the mean * S.E.M. for 5 animals.
90
cellulose and a cereal-based diet in tissue weight, crypt length, number of crypt cells and the crypt cell proliferation rate [39]. Discussion The safety of exogenous cellulose has been reviewed and updated based on literature published since the 1972 GRAS declaration. The studies discovered were not purposefully directed at testing the safety of exogenous However, exogenous cellulose per se. cellulose has been included in the diets of laboratory animals where reproductive and carcinogenic effects have been evaluated. A review of this work continues to support the safety of exogenous cellulose as no adverse effects have been discovered. Several studies demonstrate that exogenous cellulose does not display promotional activity in colon, mammary, or bladder tumor models in rats. These studies included doses as high as 46% exogenous cellulose in the diet without evidence for adverse effects. However, there remains the potential influence of caloric restriction to delay the temporal development of tumors. So these studies should be considered directional and not conclusive proof for the safety of exogenous cellulose. Exogenous cellulose has been administered in the diets of at least two valid bioassays without showing adverse effects [8, lo]. In these cases, the administered doses were not high: 3% and 5% of the diet. While these doses remove any confounding influence from caloric restriction, they are not the maximum doses desired to conclusively prove safety. Exogenous cellulose is somewhat unique in that chronic ingestion has occurred over the entire natural lifespan in both rats and mice. Under these conditions, there is no evidence for any increase in the development of spontaneous disease or neoplasia rates in either species. Other endpoints and test systems also show no apparent adverse effect from exogenous cellulose. Several studies indicate that exogenous cellulose does not adversely effect
reproduction or neonatal development in rats and mice. In the gastrointestinal tract, exogenous cellulose does not adversely alter either cell kinetics or cell morphology in either rats or mice. Furthermore, no evidence exists that cellulose adversely effects the absorption or the metabolism of dietary constituents. In summary, a variety of studies in laboratory animals demonstrate that the ingestion of exogenous cellulose does not lead to any adverse health effects. Given the variety of test systems, the range of doses, the oral route of exposure and the extended exposure times in these animal studies, no adverse health effects are anticipated for human exposure to exThis conclusion is ogenous cellulose. reinforced by the knowledge that most contact with cellulose, such as hygiene products or paper, is via short-term dermal exposure. Therefore, the available data indicate that there are no evident concerns for human safety from these products. References Reeve, D.W. and Weishar, K.M. (1990) Chlorinated organic matter in bleached chemical pulp production. Part IV: The occurrence of chlorinated organic matter in bleached pulp. J. Pulp Paper Sci., 16, J118- 5125. Sixta, H., Baldinger,T., Gotzinger, G., Mayrhofer, J., Manetsgruber, R., Vorderderffer, B. and Lindquist, L. (1990) Causes and influences of organochlorine compound burden in sulfite pulps. Lenzinger Berichte, 71, 53-58. United States Consumer Safety Product Commission. (1990) Assessment of health risks associated with exposure to paper products. Staff memorandum to the Commission, April 30, 1990. p. 73. Her Majesty’s Stationary Qffice. (1989) Dioxins in the environment. Pollution paper No. 27, Department of the Environment. Central Directorate of Environmental Protection. 45 pp. Anonymous. (1972) GRAS (Generaffy Recognized as Safe) Food Ingredients - Cellulose and Derivatives. NTIS, TR-72-1552-14. Hendrich, S.. Campbell, H.A. and Pitot, H.C. (1987) Quantitative stereological evaluation of four histochemical markers of altered foci in multistage hepatocarcinogenesis in the rat. Carcinogenesis, 8, 1245- 1250. McCollister, S.B., Kociba, R.J. and McCollister, (1973) Dietary feeding studies of methylcellulose hydroxypropylmethylcellulose in rats and dogs. Cosmet. Toxicol., 11, 943 - 953.
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response of male rats to dietary sodium saccharin. Food Chem. Toxicol., 25, 271-275. Anderson, R.L.. Lefever, F.R. and Maurer, J.K. (1988) Comparison of the responses of male rats to dietary sodium saccharin exposure initiated during nursing with responses to exposure initiated at weaning. Food Chem. Toxicol., 26, 899-907. Cummings, J.H. (1982) Consequences of the metabolism of fibers in the human large intestine. In: Dietary Fiber in Health and Disease, pp. 9- 22. Editors: G.V. Vahouny and D. Kritchevsky. Plenum Press, New York.
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glucose tolerance in humans. In: Dietary Fibers: Chemistry and Nutrition, pp. 173- 191. Editors: G.E. lnglett and S.I. Falkhag. Academic Press, New York Kritchevsky, D. (1982) Fiber and lipids. In: Dietary Fiber in Health and Disease, pp. 187- 192. Editors: G.V. Vahouny and D. Kritchevsky. Plenum Press, New York. Tsai. R.C.Y. and Lei.. K.Y. (1979) Dietary cellulose, zinc and copper: effects on tissue levels of trace minerals in the rat. J. Nutr., 109, 1117-1122. Wood, F.E. and Stall, S.J. (1991) Effect of dietary guar gum and cellulose on mineral excretion and status in young male Fischer 344 rats. Nutr. Res., 11. 621-632. Cassidy. M.M., Lightfoot, F.G. and Vahouny, G.V. (1982) Dietary fiber, bile acids and intestinal morphology. In: Dietary Fiber in Health and Disease, pp. 239- 264.
92
Editors: G.V. Vahouny 38
and D. Kritchevsky.
Plenum Press,
New York. Lupton, J.R., Coder, D.M. and Jacobs, L.R. (1988) Long-term effects of fermentable fibers on rat colonic pH and epithelial cell cycle. J. Nutr., 118, 840 - 845.
39
Goodlad, R.A. and Wright, N.A. (1983) Effects of addition of kaolin or cellulose to an elemental diet on intestinal ceil proliferation in the mouse. Br. J. Nutr., 50, 91-98.
a3 Ltd.
Review Letter
The toxicity animals R.L.
Andersona,
“1004A Celestial, 45224-1788
of purified
J.W.
Cincinnati,
(USA)
and
Owensb OH 45202,
‘Procter
&
and ‘Procter Gamble
cellulose
C.W.
in
studies
with
laboratory
Timmsc
& Gamble Paoer Products, Strasse GmbH, Sulbzocher
6200
Center
40,
D-6231
Hi/f Road, Cincinnati, Schwalbach
am
OH
Taunus
(Germany) (Received 13 October 1991) (Revision received 27 January (Accepted 28 January 1992)
1992)
Summary
Introduction
The available literature has been reviewed for studies in laboratory animals using purified of purified cellulose, as the production cellulose may result in trace organochlorine The chronic ingestion of contamination. purified cellulose over the entire lifespans in rats and mice does not result in any increase in spontaneous disease or neoplasia. Further, purified cellulose does nor display promotional activity in the mammary gland, the colon, or the bladder of rats and does not significantly alter the absorption or the metabolism of dietary components. No adverse effects were found on reproduction or neonate development in rats and mice. Therefore, no adverse health effects in humans are expected from exposure to purified cellulose.
The industrial production of cellulose is based on the removal of lignin and hemicellulose from wood to yield a purified cellulose for use in a wide array of products. Historically, molecular chlorine has been used lignin, resulting in to remove trace organochlorine residuals in the fiber. Measured as elemental chlorine, water and organic solvents extract an average of 250 ppm chlorine from softwood fiber [1,2]. Risk assessments have been performed only for individual compounds such as 2,3,7,8tetrachloro-dibenzo-p-dioxin (TCDD) [3,4]. Further, no comprehensive review of cellulose safety has occurred since 1972 when purified cellulose was declared to be generally recognized as safe (GRAS) by the United States Food and Drug Administration based upon a review of research between 1920 and 1972 [5]. For purified cellulose, the primary public health concern is carcinogenesis, focusing on the organochlorine residuals which include TCDD, a well-known carcinogen (6 and Refs.
Keywords: cellulose; ganochlorines;
diet; neoplasia; reproduction; promotion
Correspondence to: J.W. Owens, Procter Products, 6100 Center Hill Road, Cincinnati,
or-
& Gamble Paper OH 45224-1788,
USA.
0304-3835/92/$05.00 Printed and Published
0 1992 Elsevier Scientific Publishers in Ireland
Ireland
Ltd
84
therein). This review searched for animal studies from the published literature where industrially purified cellulose has been added to the diet as either an inert ingredient or as a diluent. These studies are appropriate for a safety evaluation since many of the chlorinated impurities in purified cellulose have not been identified and valid bioassays do not exist for the identified compounds. Therefore, the actual complex mixture of residuals is evaluated rather than estimating the interaction of individual, identified compounds. For clarity, this material is described as exogenous cellulose to distinguish it from natural plant or endogenous cellulose present in cereals included in chow diets. Oral administration studies using exogenous, purified cellulose were found to assess: (1) alteration of tumor expression in animal models (promotion), (2) responses in chronic, lifetime ingestion studies while monitoring spontaneous disease and neoplasms in both rats and mice and (3) reproduction and neonate development. These chronic studies either directly included chow based diets or chow based studies were available for comparison using the same animal strains. Therefore, a weight of the evidence review of this published literature was undertaken. The literature was also reviewed for other mechanisms which could influence chronic studies: (1) inhibition of digestive enzymes, (2) the metabolism of dietary components and (3) the morphology and structure of the gastrointestinal (GI) tract. Chronic
exposure
studies
with
exogenous
cellulose
The 1972 a GRAS document reviewed chronic cellulose feeding studies and concluded that there were no indications for adverse effects on human health. However, the longest laboratory animal feeding study available was 18 months. No recent studies were found specifically testing the effect of chronic exogenous cellulose ingestion on spontaneous disease development in laboratory animals. Studies of a purified cellulose derivative,
methylcellulose, were found using Sprague Dawley rats in a 2-year feeding study at 0%) 1% and 5% concentrations. The results indicated no evidence for differences in spontaneous disease rates or neoplasia from the ingestion of this cellulose derivative [7]. The largest study utilizing exogenous cellulose was by Maurer et al. [8] who conducted a bioassay of dietary sodium fluoride. Two diets were used: Purina Chow and a 5% exogenous cellulose-containing semipurified diet with a control group and three sodium fluoride groups. The study employed groups of 20 rats of each sex per treatment for interim sacrifices and 50 rats of each sex per treatment designated for the chronic exposure so that the a total of 400 animals received the exogenous cellulose diet in chronic exposures. Survival of the females but not the males was greater on the Purina Chow. Comparing Purina Chow to the 5% exogenous cellulose-containing diets, gross and histological evaluations indicated that exogenous cellulose was not associated with any increase in the incidence or severity of either non-neoplastic or neoplastic lesions. Spontaneous renal mineralization and an increased incidence of hepatocyte vacuolar changes were the result of high caloric intake and rapid growth and not a function of cellulose ingestion per se. Caloric restriction with constant cellulose ingestion prevents the expression of both of these lesions [9] (see Tables 1 and 2). In a second study, Anastasia et al. [lo] compared a Purina Chow to two semi-purified diets containing 3% purified cellulose (Celluflour) ( - 1.2 g cellulose/kg body wt. per day). The diets were fed ad libitum to groups of 50 rats per sex with scheduled sacrifices at 3, 6, 12 and 22 months. The semi-purified diets resulted in greater total weight gain with lower relative organ weights (g/100 g body wt.) as absolute organ weights were higher in cellulose-fed groups. Histopathology differences were limited to enhanced kidney mineralization in semi-purified diet females and to diffuse perinuclear hepatocyte vacuolization in the semi-purified diet males.
85 Table 1. Effect of caloric restriction on chronic nephropathy in male rats ingesting diets containing purified cellulose. Nephropathy grade ’
% Incidence Ad libitum
0 1 2 3 4 E
(1211
Restricted (106)
4 8 15 20 21 32
16 66 13 3 0 2
The study employed male, containing 3% exogenous or restricted to 60% of the group. Values for animals dying spontaneously. Data ‘Higher numbers indicate stage. Values in parantheses
Fisher 344 rats ingesting a diet cellulose fed either ad libitum caloric intake of the ad libitum killed at interim sacrifices and derived from Maeda et al. [9]. more severe lesions. E, endrepresent number of animals.
Both of these findings were previously reported in rats ingesting semi-purified diets and were not considered significantly related to exogenous cellulose consumption [ 111. The percentage incidence of neoplasms and
Table 2. Effect of caloric restriction on fatty changes in the liver of rats ingesting diets containing purified cellulose. Fatty change grade ’
0 1 2 3
% Incidence Ad libitum
Restricted
(121)
(106)
27 45 21 7
66 25 9 0
Results include animals from scheduled sacrifices and dying spontaneously. Values in parentheses represent number of animals. See Table 1 for dietary details. Data derived from Maeda et al. [9]. ‘Higher numbers indicate more severe lesions.
specific neoplasm types did not differ significantly between the chow diet and either of the cellulose-containing diets. The authors concluded that the semi-purified diets containing exogenous cellulose did not significantly alter the health of the rats. Caloric
restriction
studies
Exogenous cellulose has been a dietary component in chronic feeding studies evaluating spontaneous disease and neoplasia during lifetime caloric restriction. Lifetime caloric restriction increases longevity and delays the expression of spontaneous disease, including an apparent increase in the latency period for neoplasia (see Ref. 12 for a review). For example, lifetime caloric restriction studies were conducted using male Fischer 344 rats ingesting a diet containing 3% exogenous cellulose (Solka Floe). These rats were maintained in a barrier restricted environment to prevent infection until either scheduled interim sacrifices or death [9]. One group consumed their diet ad libitum, while intake in another group was restricted to 60% of that of the ad libitum group as described by Yu et al. [13]. The groups consumed equivalent nutrients over their lifetime (36.3 x lo3 kcal/rat for the ad libitum vs. 35.7 x lo3 kcal/rat for the restricted group) and equivalent amounts of exogenous cellulose (- 270 g/rat). Due to the difference in body weights, the daily relative dose of cellulose was also equivalent at - 1 g/ kg body wt. per day. Caloric restriction was associated with less disease and a delay in the expression of disease at the three primary sites (kidney, liver and heart) noted in the rats fed ad libitum [9]. In terms of neoplasms, the restricted group displayed a marked delay in the appearance of neoplasms, but the total lifetime incidence of neoplasms was unchanged (Table 3). To further assess the interplay of caloric restriction and exogenous cellulose ingestion, the above described rats can be compared with rats of the same strain consuming a cerealbased diet, ad libitum for up to 33 months [14]. The principle causes of death in both
86 Table 3.
Effect of caloric restriction on the incidence of neoplasms other than testicular tumors in rats ingesting diets containing purified cellulose. Tumor classification Benign
Tumorbearing rats
Malignant % incidence
Ad Libitum (121) Restricted (106)
37
16
39
34
31
42
Sum of all tumors in animals from scheduled sacrifices and spontaneous deaths. Values in parentheses represent number of animals. See Table 1 for details. Data derived from Maeda et al. [9].
studies
advanced renal disease and Neoplasia comparisons between the rats ingesting the cereal-based diet and those ingesting the exogenous cellulosecontaining diet demonstrate a strong similarity in the time of appearance, target organ and incidence rate of neoplasms. This shows that lifetime spontaneous disease and neoplasia development are not influenced by ingesting exogenous cellulose chronically at least at a level of 3% in the diet or - 1 g/kg body wt. per day. Mice respond to dietary restriction with a similar increase in longevity and a delay in spontaneous disease [ 121. One study by Weindruch et al. [15] compared a cereal-based chow group to two groups consuming a semipurified diet containing 5.6% exogenous cellulose using females of a long-lived hybrid strain (Fr progeny from C3HSW/Sn females mated with C57BLlO.RIII/Sn males). The cellulose consuming groups were fed either 7 times per week for 15% restriction (4.6 g cellulose/kg body wt.) or 4 times per week for 50% restriction (3.1 g cellulose/kg body wt.). Mean lifespans were 27.4 months for ad libitum, chow-fed mice, 32.7 months for the cellulose-containing diet fed 7 times per week neoplasms.
were
and 42.3 months for the cellulose-containing diet fed 4 times per week. Lifetime cancer incidence was not influenced by either the caloric intake or exogenous cellulose in the diet. Although the onset of neoplasms was delayed in the caloric-restricted mice, no difference in survival rates or survival times after tumor onset occurred. Therefore, the lifetime ingestion of exogenous cellulose does not alter the incidence of spontaneous disease or neoplasms in either mice or rats, providing no evidence for carcinogenic activity. The liver is an organ of special interest as a primary site of toxicity with many halogenated organics. In this regard, the spontaneous liver pathology in male Fischer-344 rats allowed to live their maximal lifespan while ingesting either a cereal-based diet [14] or a semipurified diet containing 3% exogenous cellulose (Solka Floe) [9] can be compared. All of these animals showed similar liver pathology and the incidence of liver tumors was always less than 1% . This reinforces the evidence that exogenous cellulose and its residuals after lifetime ingestion do not display either promotional or carcinogenic activity in the liver. No studies were found in the literature directly comparing exogenous cellulose from processes with and without molecular chlorine. However, molecular chlorine bleaching of wheat flour has been tested in chronic ingestion studies in both rats 1161 and mice [17]. Bleached wheat flour containing residuals with 1250 and 3000 ppm organically-bound chlorine comprised 30% of the diet in both studies. In addition, two control diets were used in both studies: an unbleached flour containing diet and a cereal-based diet. The unbleached flour containing diet provides the higher caloric density of flour to act as a control versus the cereal-based diet. Rats were fed these diets for 104 weeks and mice for 17 months. When compared to the cerealbased diets, both higher caloric, flour-based diets decreased the survival of female rats, but not males. No differences were observed between the organochlorine containing bleached and the unbleached group in longevity,
87
spontaneous disease, or incidence of neoplasia for any tissue in either rats or mice. Exogenous cellulose and tumor models If exogenous cellulose residuals had cancer promoting activities, then the assumption is that diets containing exogenous cellulose should lead to an increased cancer rate when administered subsequent to a dose of a sitespecific carcinogen. Studies designed to determine the effect of high-fat diets on tumor promotion in the GI tract and in the breast of experimental animals have employed a broad range of dietary exogenous cellulose levels. Exogenous cellulose does not display tumor promotion activity on the colon at large doses. In rats, 10 -30% exogenous cellulose in the diet has been ingested for 24 weeks after exposure to azoxymethane (AOM) to induce large bowel tumors. Tumor rates in animals ingesting exogenous cellulose were lower comcompared to the fiber-free controls (Table 4) [18]. In a second study, rats induced with dimethylhydrazine (DMH) consumed diets containing 0% , 4.5%, or 9% exogenous cellulose. Again, the groups ingesting exogenous cellulose had a lower incidence of colon tumors than the group consuming a cellulose-free diet. Tumor rates in the small bowel also decreased, but did not attain statistical significance [ 191. Newberne and Schrager (1991) have summarized the effects of cellulose on experimentally induced colo-
Table 4. Effect of purified cellulose ingestion on the incidence of large bowel tumors in rats exposed to azoxymethane. Average tumors/rat
Diet
Fiber-free + 35% 10% Cellulose + Fiber-free + 6% 20% Cellulose + 30% Cellulose +
tallow 35% tallow tallow 6% tallow 6% tallow
8.44 7.88 4.04 2.86 1.95
Data are taken from Nigro et al. [18]
rectal tumors in rodents, noting no adverse effect in six studies and in only one study was there an enhancement [20]. Additional exogenous cellulose feeding studies have used the rat mammary gland as a carcinogenic target with similar results. Kritchevsky et al. [21] fed rats diets containing 8 - 46 % exogenous cellulose with different levels of fat for mammary tumor promotion for 120 or 134 days after exposure to dimethylbenzanthracene (DMBA). With constant caloric intake, cellulose levels (12% and 32%) in the diet fed after initiation were without effect on tumor incidence. Further, a high-fat, ad libitum diet fed with high levels of cellulose (46%) resulted in a lower tumor incidence than a low-fat diet with a low level of cellulose (8%). Finally, caloric restriction at constant mineral and cellulose ingestion rates resulted in a 0% incidence of mammary tumor compared to 58% for the non-restricted group ingesting the equivalent amounts of purified cellulose [21]. In a second study, the effect of caloric restriction was tested on mammary tumorigenesis in DMBA-exposed female rats and colon tumorigenesis in DMH-exposed male rats. The control and restricted animals consumed the same amounts of cellulose and a lower tumor incidence was observed at both sites at equivalent cellulose intake levels (Table 5) [22]. In a third study, the effect of caloric intake on DMBA tumorigenesis in female F344 rats was studied using diets containing 5% cellulose with 5% and 30% corn oil. The mammary tumor incidences on these diets were 75%) 8% and 42 % at cellulose intakes of 2.2 g/kg (30% corn oil, ad libitum) , 2.1 g/kg (30% corn oil, restricted) and 3.4 g/ kg (5% corn oil ad libitum) , respectively [23]. Thus, in no case was mammary tumorigenesis proportional to cellulose ingestion, but was highly correlated only with caloric intake. In addition, the bladder was the target for promotional studies of sodium ascorbate and sodium saccharinate in conjunction with exogenous cellulose diets. Tumorigenesis was reduced when these salts were fed in a semipurified diet (AIN-76) containing 5%
88 Table 5. cellulose.
Effect of caloric restriction
on mammary
Ad libitum DMBA induced mammary Tumor incidence (%) Total tumor yield (W) Mean tumor weight (g)
tumors 80 64 2.8
DMH induced colon tumors Tumor incidence (46) Total tumor yield (W) Data are taken from Kritchevsky
l
1.1
100 63
and colon tumorigenesis
Restricted
Statistic
20 4 0.2*0.1
P < 0.001 P c 0.001 P < 0.01
53 20
P < 0.001 P < 0.001
purified
et al. [21].
exogenous cellulose versus a Purina Chow diet [24]. Therefore, the available evidence suggests that exogenous cellulose residuals do not display tumor promoting activity in the mammary gland, the colon, or the bladder, when administered at high oral doses. Cellulose
in rats ingesting diets containing
effects on reproduction
and growth
The GRAS report concluded that exogenous cellulose did not induce adverse reproductive effects, based on a three generation reproductive study in rats using purified cellulose at a 30% level in the diet [5]. In subsequent studies, reproduction in both rats and mice has been compared in animals ingesting an open formula, cereal-based diet (NIH-07) and a semi-purified diet (AIN-76) containing 5% exogenous cellulose [25]. In rats bred twice and mice bred continuously, reproductive performance was comparable in terms of pups per litter, pup survival and pup growth. Teratogenic effects were not observed and growth rates in both species for up to 18 weeks after weaning were unaffected. Thus, 5% exogenous cellulose ingestion did not adversely influence either reproduction or growth and development in rats or mice. In additional growth studies, dietary levels of exogenous cellulose up to 20% by weight did not retard growth in adult rats [26,27]. In rat
pups, the effects of exogenous cellulose (Avicel-PH) at 0%, 58, 10% and 20% in the diet were studied on carcass composition in rat pups after 28 days of ad libitum ingestion. The pups ingesting the 10 and 20% cellulose diets did not increase food consumption to compensate for the caloric dilution and gained less weight [28]. In a second study, 4.8%) 9.1%) 16.7% and 28.6% exogenous cellulose was added to the diet for 4 weeks and crude protein quality was varied. At the highest dose, the cellulose containing diet did decrease carcass fat due to lower caloric intake, but all other differences were dependent upon protein quality and not the cellulose content [29]. High-calorie, high-quality protein components can compensate for caloric dilution to confirm the lack of toxicity with exogenous cellulose. Feeding 40% levels of exogenous cellulose in isocaloric, isonitrogenous diets did not effect growth when compared to a diet with 5% cellulose [30]. The growth of rat pups was only slightly decreased by ingestion of a low-carbohydrate diet containing 41% cellulose (Solka Floe) introduced at parturition to their dams and then to the pups for 10 weeks after weaning [31]. Therefore, ingestion of massive cellulose doses has no apparent adverse effect on pup growth and development in either mice or rats.
89
Exogenous
cellulose and dietary component
metabolism
Any substantive differences in nutrient metabolism might confound the interpretation of exogenous cellulose safety, especially during chronic feeding studies. Cellulose does not substantially alter the fate of glucose [32], stool lipid and stool nitrogen [33], or serum cholesterol levels 1341 in humans. Although mineral balance is potentially influenced by metal ion chelation with hydroxyl and carboxyl groups in cellulose, no detrimental effects have been observed in rats (see Table 6) [27,35,36]. Exogenous cellulose and GI tract effects As the GI tract is directly exposed to ingested cellulose and any trace residuals, the effects on intestinal structure and physiology are important endpoints for the safety evaluation
Table 6. Mineral excretion cellulose (5% C) r. Element
Diet
in young and old rats ingesting either a fiber-free
% of ingested
minerals
Urine
P Mg Fe cu Zn Mn
FF 5% c FF 5% c FF 5% c FF 5%C FF 5% c FF 5% c FF 5% c
1.3 0.8 26 19 19 15 -
6*1 4*1 0.7 f 0.2 0.5 f 0.1 < 0.1 < 0.1
5% purified
Old rats Feces
f 0.3 zt 0.3 zt 5 ztz 2 f 4 f 5
(FF) diet OT a diet containing
excreted
Young rats
Ca
of exogenous cellulose. The available data show that large doses of exogenous cellulose ingested for extended periods do not adversely alter cell morphology or cell dynamics in the GI tracts of experimental animals. In rats, a diet containing 15% exogenous cellulose (Solka Floe) did not alter the morphology of the small or large intestine compared to groups ingesting a cereal-based diet [37]. A diet containing 10% cellulose (Avicel PH-105) was compared to a fiber-free diet in rats after 35 weeks of ingestion. The exogenous cellulose did not influence body weight gain, cecal surface area or colon length, or epithelial cell cycle distribution from the proximal or distal colon. The latter finding indicated that exogenous cellulose did not alter colon cell turnover or proliferation [38]. In mice, no differences in the structure and the histology of the intestine were found between the group ingesting 30% exogenous
73 59 39 35 47 35 93 66 84 70 103 86 115 96
Urine zt 8 f 4 l 3 f 2 f 5 f 2 zt 10 l 4 f 11 f 4 f 10 l 5 l 11 f 5
2.4 * 2.1 f 28 * 22 f 21 f 20 f 8&l 7*1 1.3 f 1.0 f 0.3 * 0.2 f
Feces 0.3 0.2 2 2 2 2
0.2 0.1 0.06 0.04
103 93 58 57 63 46 93 87 66 61 96 86 104 92
l 5 zt 4 + 3 f 2 ziz 3 f 2 ziz 4 ztz 4 f 4 zt 3 f 5 f 3 f 5 zt 4
The study employed male, Fischer 344 rats ingesting a purified diet (AIN-76A) containing either no fiber or 5% cellulose. The young rats were -3 weeks past weaning (data are from Wood and Stall 1361) and the old rats were 21 months old (Wood, unpublished data). ‘Each value is the mean * S.E.M. for 5 animals.
90
cellulose and a cereal-based diet in tissue weight, crypt length, number of crypt cells and the crypt cell proliferation rate [39]. Discussion The safety of exogenous cellulose has been reviewed and updated based on literature published since the 1972 GRAS declaration. The studies discovered were not purposefully directed at testing the safety of exogenous However, exogenous cellulose per se. cellulose has been included in the diets of laboratory animals where reproductive and carcinogenic effects have been evaluated. A review of this work continues to support the safety of exogenous cellulose as no adverse effects have been discovered. Several studies demonstrate that exogenous cellulose does not display promotional activity in colon, mammary, or bladder tumor models in rats. These studies included doses as high as 46% exogenous cellulose in the diet without evidence for adverse effects. However, there remains the potential influence of caloric restriction to delay the temporal development of tumors. So these studies should be considered directional and not conclusive proof for the safety of exogenous cellulose. Exogenous cellulose has been administered in the diets of at least two valid bioassays without showing adverse effects [8, lo]. In these cases, the administered doses were not high: 3% and 5% of the diet. While these doses remove any confounding influence from caloric restriction, they are not the maximum doses desired to conclusively prove safety. Exogenous cellulose is somewhat unique in that chronic ingestion has occurred over the entire natural lifespan in both rats and mice. Under these conditions, there is no evidence for any increase in the development of spontaneous disease or neoplasia rates in either species. Other endpoints and test systems also show no apparent adverse effect from exogenous cellulose. Several studies indicate that exogenous cellulose does not adversely effect
reproduction or neonatal development in rats and mice. In the gastrointestinal tract, exogenous cellulose does not adversely alter either cell kinetics or cell morphology in either rats or mice. Furthermore, no evidence exists that cellulose adversely effects the absorption or the metabolism of dietary constituents. In summary, a variety of studies in laboratory animals demonstrate that the ingestion of exogenous cellulose does not lead to any adverse health effects. Given the variety of test systems, the range of doses, the oral route of exposure and the extended exposure times in these animal studies, no adverse health effects are anticipated for human exposure to exThis conclusion is ogenous cellulose. reinforced by the knowledge that most contact with cellulose, such as hygiene products or paper, is via short-term dermal exposure. Therefore, the available data indicate that there are no evident concerns for human safety from these products. References Reeve, D.W. and Weishar, K.M. (1990) Chlorinated organic matter in bleached chemical pulp production. Part IV: The occurrence of chlorinated organic matter in bleached pulp. J. Pulp Paper Sci., 16, J118- 5125. Sixta, H., Baldinger,T., Gotzinger, G., Mayrhofer, J., Manetsgruber, R., Vorderderffer, B. and Lindquist, L. (1990) Causes and influences of organochlorine compound burden in sulfite pulps. Lenzinger Berichte, 71, 53-58. United States Consumer Safety Product Commission. (1990) Assessment of health risks associated with exposure to paper products. Staff memorandum to the Commission, April 30, 1990. p. 73. Her Majesty’s Stationary Qffice. (1989) Dioxins in the environment. Pollution paper No. 27, Department of the Environment. Central Directorate of Environmental Protection. 45 pp. Anonymous. (1972) GRAS (Generaffy Recognized as Safe) Food Ingredients - Cellulose and Derivatives. NTIS, TR-72-1552-14. Hendrich, S.. Campbell, H.A. and Pitot, H.C. (1987) Quantitative stereological evaluation of four histochemical markers of altered foci in multistage hepatocarcinogenesis in the rat. Carcinogenesis, 8, 1245- 1250. McCollister, S.B., Kociba, R.J. and McCollister, (1973) Dietary feeding studies of methylcellulose hydroxypropylmethylcellulose in rats and dogs. Cosmet. Toxicol., 11, 943 - 953.
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8
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(1982) Development of hepatic lesions in male Fischer 344 rats fed AIN076A purified diet. Toxicol. Appl. Pharmacol.. 62, 111-120. Weindruch, R. and Walford, R.L. (1988) The retardation of aging and disease by dietary restriction. Charles C. Thomas, Springfield, IL. Vu, B.P., Masoro, E.J. and McMahan, C.A. (1985) Nutritional influences on aging in Fischer 344 rats: I. Physical,
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cinogenicity studies of cake made from chlorinated flour. I. Studies in rats. Food. Chem. Toxicol., 21, 427-434. Ginocchio, A.V., Fischer, N., Hutchinson, J.B. Berry, R. and Hardy, J. (1983) Long-term toxicity and car-
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with cake made from chlorinated flour. Food. Chem. Toxicol., 21, 435-439. A.W., Klopfer, B.A., Pak, M.S. and (1979) Effect of dietary fiber on
azoxymethane-induced intestinal carcinogenesis in rats. J. Natl. Cancer Inst., 62, 1097 - 1116. Freeman, H.J. (1982) Studies on the effect of single fiber sources in the dimethylhydrazine rodent model of human bowel neoplasia. In: Dietary Fiber in Health and Disease, pp. 287 - 297. Editors: G.V. Vahouny and D. Kritchevsky. Plenum Press, New York. Newberne. P.M. and Schrager. T.F. (1991) Nutritional promoters and inhibitors of carcinogenesis. and Molecular Basis of Acquired Disease, Editors: L.B. Alberti and A. Dewman. Toudall, London.
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male rats.
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In: Metabolic pp. 74-97. Bailliere and
Kritchevsky, D., Weber, M.M. and Klurfeld, D.M. (1984) Dietary fat versus caloric content in initiation and promotion of 7.12-dimethylbenz[o]anthracine-induced mammary tumorigenesis in rats. Cancer Res., 44, 3174-3177. Kritchevsky,
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D.M. (1986) Calories, fat and cancer. Lipids, 21, 272 - 274. Boissonneault, G.A., Elson, C.E. and Pariza, M.W. (1986) Net energy effects of dietary fat on chemically induced mammary carcinogenesis in F344 rats. J. Natl. Cancer Inst., 76, 335 - 338. Anderson, R.L. (1989) High dose sodium toxicity. Cancer Lett., 48, 1- 11. Bieri, J.G., Stoewsan, G.S., Briggs, G.M., Phillips, R.W., Woodward. J.C. and Knapka, J.J. (1977) Report of the American institute of Nutrition ad hoc committee on standards in nutritional studies. J. Nutr.. 107. 1340- 1348. Hove. E.L. and King, S. (1979) Effects of pectin and cellulose in growth, feed efficiency and protein utilization and their contribution to energy requirements and cecal VFA in rats. J. Nutr., 109. 1274- 1278. Gordon, D.T. (1990) Total dietary fiber and mineral absorption. In: Dietary Fiber: Chemistry, Physiology and Health Effects, pp. 105 - 208. Editors: D. Kritchevsky, C. Bonfield and J.W. Anderson. Plenum Press, N.Y. Sundaravalli, O.E.. Shurpalekar. K.S. and Rao, M.N. (1971) Effects of dietary cellulose supplements on the body composition and cholesteroi metabolism in rats. J. Agric. Food Chem., 19. 116- 118. Wojcik, J. and Delorme, C.B. cellulose cass and Int., 27. Anderson, Effect of
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