Dig Dis Sci (2010) 55:3078–3085 DOI 10.1007/s10620-010-1158-9
ORIGINAL ARTICLE
Naturally Occurring Glycoalkaloids in Potatoes Aggravate Intestinal Inflammation in Two Mouse Models of Inflammatory Bowel Disease Vadim Iablokov • Beate C. Sydora • Rae Foshaug • Jon Meddings • Darcy Driedger • Tom Churchill • Richard N. Fedorak
Received: 20 May 2009 / Accepted: 7 December 2009 / Published online: 3 March 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Background Inflammatory bowel disease (IBD) may be initiated following disruption of the intestinal epithelial barrier. This disruption, in turn, permits luminal antigens unfettered access to the mucosal immune system and leads to an uncontrolled inflammatory response. Glycoalkaloids, which are found in potatoes, disrupt cholesterol-containing membranes such as those of the intestinal epithelium. Glycoalkaloid ingestion through potatoes may play a role in the initiation and/or perpetuation of IBD. Aim To determine if commercial and high glycoalkaloids containing fried potato skins aggravate intestinal inflammation using two different animal models of IBD. Methods Fried potato skins from commercial potatoes containing low/medium glycoalkaloid levels and high glycoalkaloids potatoes were fed for 20 days to interleukin 10 gene-deficient mice and dextran sodium sulfate-induced colitic mice. Intestinal permeability, mucosal cytokine and myeloperoxidase levels and body weight were determined to assess intestinal injury.
Results Deep frying potato skins markedly increased glycoalkaloid content. Interleukin 10 gene-deficient mice fed fried commercial potato skins with medium glycoalkaloid content exhibited significantly elevated levels of ileal IFN-c relative to controls. Mice in the dextran sodium sulfate colitis model that were fed the same strain of potatoes demonstrated significantly elevated levels of proinflammatory cytokines IFN-c, TNF-a, and IL-17 in the colon in addition to an enhanced colonic permeability. Inflammatory response was intensified when the mice were fed potatoes with higher glycoalkaloid contents. Conclusions Our results demonstrate that consumption of potato skins containing glycoalkaloids can significantly aggravate intestinal inflammation in predisposed individuals. Keywords Glycoalkaloid Inflammatory bowel disease Crohn’s disease Ulcerative colitis Intestinal permeability Mucosal inflammation
Introduction V. Iablokov (&) B. C. Sydora R. Foshaug J. Meddings R. N. Fedorak Division of Gastroenterology, University of Alberta, Zeidler Ledcor Building, Edmonton, AB T6G 2X8, Canada e-mail:
[email protected] R. N. Fedorak e-mail:
[email protected] T. Churchill Department of Surgery, University of Alberta, Edmonton, AB, Canada D. Driedger Alberta Agriculture and Rural Development, Brooks, AB, Canada
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The intestinal epithelium provides a barrier between potentially toxic agents within the lumen and the exquisitely sensitive mucosal immune system [1]. Inflammatory bowel disease (IBD) is thought to occur as a consequence of altered mucosal barrier integrity coupled with an inability to appropriately regulate mucosal inflammatory responses [2]. While the altered mucosal barrier integrity, if primary, is likely determined by genetic factors, barrier integrity can also be compromised through exogenous agents within the lumen of the gastrointestinal tract [3, 4]. The modern cultivated potato (Solanum tuberosum L.) represents one of the world’s major agricultural crops and
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is grown in approximately 80% of all countries. Potatoes contain glycoalkaloid poisons that are concentrated in the leaves, stems, potato skin, and adjacent 1.5-mm periderm. These glycoalkaloids are a major contributor to the potato’s bitter taste [5]. Glycoalkaloids (GA) are a family of poisons commonly found in the deadly nightshade family and are part of a plant’s defense mechanism against pests and microbial pathogens [6]. Ninety-five percent of all glycoalkaloid content in potatoes is represented by a mixture of more toxic a-chaconine and less toxic a-solanine [7]. Exposure to light, physical damage such as frying, high temperature storage, and age increase glycoalkaloid content within the tuber. The glycoalkaloid levels in high GA potatoes ([100 mg glycoalkaloid/100 g potato) can result in serum levels of 3–6 mg GA/kg body weight and be fatal to humans. As such breeders must show that new potato varieties contain less than 20 mg/100 g before the variety can be released. Systemic toxic effects include gastrointestinal injury with vomiting and diarrhea, tachycardia, hemolysis, headache, and neurotoxicity with subsequent death [7]. These toxic effects are mediated by the ability of GA to inhibit acetyl cholinesterase activity as well as bind to 3b-hydroxy sterols and disrupt sterol-containing membranes, such as those of the intestinal epithelia [6, 8]. Using purified GA we have previously shown that exposure to a 1:1 a-chaconine: a-solanine mixture resulted in disruption of a T84 monolayer in vitro [9]. Epithelial barrier disruption by the combined glycoalkaloid mixture was enhanced relative to exposure by either a-chaconine or a-solanine individually. The same purified 1:1 glycoalkaloid mixture, when administered in drinking water, was shown to alter epithelial barrier integrity and to worsen colonic histological injury scores in interleukin (IL) 10-gene-deficient mice [9]. In the current study we investigated whether oral ingestion of naturally occurring glycoalkaloids contained in potatoes could alter intestinal permeability and worsen the intestinal injury associated with IBD.
Materials and Methods Mice Two separate animal IBD models were used in the experiments. The dextran sodium sulfate (DSS) chemically induced mouse model of IBD [10, 11], and the IL-10 genedeficient predisposed mouse model of IBD [12]. Genetically Predisposed IBD Model Male IL-10 gene-deficient mice (129/SvEv background) were from a colony housed at the University of Alberta
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animal facility under specific pathogen-free conditions. All mice used were 10 weeks of age at the start of the experiment. This age is approximately 4 weeks prior to the onset of spontaneous IBD in this colony of IL-10 gene-deficient mice. Chemically Induced IBD Model DSS-induced colitis was initiated in 129/SvEv mice at 10 weeks of age. Mice received 1% w/v DSS in their drinking water for 8 days, allowed to recover for 3 days without DSS supplementation, and then 0.2% w/v DSS in the drinking water was resumed for an additional 8 days. DSS was given to the mice at suboptimal concentrations to allow for a possible additive effect on colitis development in mice treated with both DSS and GA-containing fried potatoes. Potato Skin Preparation Commercial Potatoes Commercially purchased, organic potatoes (Top Brass Potatoes, Vignolo Farms, Shafter, United States) were peeled to yield the skin and 5 mm of periderm (i.e., that portion of the potato commonly sold in restaurants as ‘‘potato skins’’). To mimic human potato skin ingestion, the above peeled product was fried at 130°C in 100% canola oil (Western Family, Vancouver, Canada) in a deep fryer (Esclusivo, DeLonghi, Mississauga, Canada) for 12 min [13]. These commercial potato skins yielded, in the raw nonfried state, glycoalkaloid levels of 15.4 mg glycoalkaloids/ 100 g potato, a level that is within the regulated acceptable range of less than 20 mg glycoalkaloid/100 g potato. High-GA Potatoes A non-commercial breeding line of Solanum tuberosum potatoes known for its high glycoalkaloid levels was obtained from Alberta Agriculture and Rural Development (Brooks, AB, Canada). These ‘‘high-GA potatoes’’ were peeled and prepared in the identical manner as described above. These potato skins yielded, in the raw non-fried state, total glycoalkaloid levels of 46.0 mg glycoalkaloids/100 g potato, a level that is well above the regulated acceptable range of less than 20 mg glycoalkaloid/100 g potato. Glycoalkaloid Measurement Glycoalkaloids in the potato skins, before and after deep frying, were determined by HPLC at the Alberta Agriculture and Rural Development laboratory. Briefly, a-Solanine and a-chaconine levels were measured using AOAC International method 997.13 modified for dry samples [14].
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The procedure involved extracting dry potato material with acetic acid and sodium bisulfite, cleaning the extract with a C18 solid-phase extraction cartridge and performing HPLC with a C18 column and UV detection at 202 nm [14]. Potato-Fed Experimental Groups Mice were not fed raw potato skins; instead, all potato skins used in the experiments were freshly prepared on the day of feeding by deep frying as outlined above. Fried potato pieces were placed on a dish inside the mouse cages. Mice were allowed to consume potatoes ad libitum. No chow or other mouse feed was provided for the duration of the experiments, however, all mice received a similar quantity of dietary supplement (Bio-Serve Liquid Rat Supplement, Frenchtown, USA) for the study duration to ensure similar nutrient intake between each group. Experiment 1: Genetically Predisposed Mouse Model of IBD IL-10 gene-deficient mice were fed freshly prepared fried commercial potato skins for 20 days. IL-10 gene-deficient mice used as controls were fed standard mouse chow. Killing and analysis was performed on day 20.
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During the urine collection, mice had ad libitum access to distilled drinking water. After 22 h of collection, urine weight was recorded and HPLC analysis performed to identify individual carbohydrate concentrations as described previously [15]. An increase in the ratio of urinary lactulose to mannitol indicated a defect in small-intestinal epithelial integrity; while an increase in urinary sucralose indicated a defect in colonic epithelial integrity [15]. Measurement of Intestinal Cytokine and Myeloperoxidase Levels Mucosal cytokine and intestinal myeloperoxidase (MPO) levels were determined at time of killing. Five centimeters of ileum and the entire 10 cm of colon were excised, cut longitudinally and individually cultured for 24 h in 1 ml complete RMPI solution containing 5% fetal calf serum (Life Technologies, Burlington, Canada) [16]. Mucosal release of pro-inflammatory cytokines (TNF-a, IFN-c, and IL-17) as well as myeloperoxidase levels in the culture supernatants were quantified by standard cytokine-specific ELISA procedures using commercially available kits (BD Biosciences, San Diego, Cell Sciences, for TNF-a, IFN-c and IL-17, and Canton, MA, USA for MPO). Body Weight
Experiment 2: Chemically Induced Mouse Model of IBD DSS-induced colitis mice were fed the same freshly prepared fried commercial potato skins as in experiment 1 for 20 days concomitantly with the DSS treatment. Controls consisted of DSS-treated mice fed standard mouse chow and non-DSS-treated mice fed fried commercial potato skins or normal chow. To examine the concentrationdependant effect of GAs on cytokine levels in this model, DSS-treated mice were fed freshly prepared fried high-GA potato skins in an additional experiment. Controls consisted of DSS-treated mice fed standard mouse chow and non-DSS-treated mice. Killing and analysis for both trials was performed on day 20. Assessment of Small-Intestinal and Colonic Permeability Intestinal permeability was assessed by a previously validated urinary sugar excretion method [15]. On the last day of potato feeding, each mouse received (via oral gavage) 200 ll of a solution containing lactulose (60 mg/ml), mannitol (40 mg/ml), and sucralose (30 mg/ml). The mice were then immediately placed in metabolic cages and urine was collected for 22 h into vials containing 30 ll of a 10% thymol solution in isopropanol and 100 ll mineral oil to prevent bacterial overgrowth and evaporation, respectively.
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Body weights of all mice were recorded daily for the duration of the experiment. Statistics Values are given as mean ± SEM. Significance in the difference of means was determined through the use of standard error-based t-tests, one-way ANOVA followed by Tukey’s post-test, and two-way ANOVA followed by Bonferroni’s post test where applicable. Significance was defined as p \ 0.05. Ethical Considerations This study was approved by the Animal Health Ethics Board at the University of Alberta.
Results Effects of Deep Frying on Potato Glycoalkaloid Concentration Commercial potatoes skins (peeled as outlined above) in the raw non-fried state had a glycoalkaloid concentration of 15.4 mg glycoalkaloid/100 g potato (9.9 mg/100 g of
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a-chaconine and 5.5 mg/100 g of a-solanine). After 12 min of deep frying at 130°C, the commercial fried potato skins had a glycoalkaloid concentration of 44.2 mg glycoalkaloid/100 g potato (28.9 mg/100 g of a-chaconine and 15.3 mg/100 g of a-solanine) (Fig. 1). Frying the commercial potato skins elevated the glycoalkaloid levels above the regulated acceptable levels of 20 mg/100 g potato. High-GA potatoes (peeled as outlined above) in the raw non-fried state had a glycoalkaloid concentration of 46.0 mg glycoalkaloid/100 g potato (24.8 mg/100 g of a-chaconine and 21.5 mg/100 g of a-solanine), well above the regulated acceptable levels. Experiment 1: Genetically Predisposed Mouse Model of IBD Cytokine and Myeloperoxidase Levels IL-10 gene-deficient mice fed fried commercial potato skins had significantly higher IFN-c levels compared to chow-fed controls (82.79 ± 21.63 versus 11.06 ± 11.06 pg/g tissue, respectively, p \ 0.01; Fig. 2). The increased IFN-c level was found in the ileum, a compartment usually with cytokine levels indistinguishable from those in wild-type mice of the same background in these IBD-prone mice. No significant increase in ileal TNF-a, IL-17 or MPO levels were detected (data not shown). There were also no increases in cytokine or myeloperoxidase levels in the colon of commercial skin potato-fed IL-10 gene-deficient mice compared to chow-fed control mice (data not shown).
Fig. 1 Glycoalkaloid, a-solanine and a-chaconine, concentration in commercial potato skins before and after deep frying and in high GA potato skins. Deep frying markedly increases glycoalkaloid levels. The dashed line represents the regulated maximum glycoalkaloid concentration in commercially sold potatoes (20 mg/100 g potato)
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Small-Intestinal and Colonic Permeability Feeding fried commercial potato skins did not cause a significant enhancement of either the small-intestinal or colonic permeability defect in IL-10 gene-deficient mice as judged by similarly high urinary lactulose/mannitol ratio and high sucralose levels when compared to those in chowfed control mice (data not shown). Body Weight IL-10 gene-deficient mice fed fried commercial potato skins showed no significant difference in weight compared to chow-fed controls at any point during the 20 day trial (data not shown). Experiment 2: Chemically Induced Mouse Model of IBD Given the fact that we were observing increased inflammatory cytokine responses upon exposure to commercial potatoes in the genetically predisposed IL-10 gene-deficient mouse model of IBD, we next examined the effect in a second IBD model and progressed to also examining the effect of potatoes with a high GA content. That is, examining a ‘‘dose’’ effect of orally ingested potato glycoalkaloids. Cytokine and Myeloperoxidase Levels In our experimental design we chose a concentration of DSS and duration of DSS treatment that by itself did not lead to extensive intestinal inflammation and mucosal
Fig. 2 IFN-c levels from ileal mucosa of IL-10 gene-deficient mice fed fried commercial potato skins (solid bar) or control standard mouse chow (open bar). Feeding fried commercial potato skins significantly elevated cytokine levels. Values represent mean ± SEM. n = 4 mice per group. (*) Compared to IL-10 gene-deficient controls fed standard mouse chow (p \ 0.05)
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damage. Accordingly, the release of inflammatory cytokines as well as the levels of intestinal MPO were increased in DSS-treated mice compared to controls; nevertheless, this increase in the average did not reach significance (Figs. 3, 4 hatched bars). However, consumption of commercial fried potatoes alone, in the absence of diseaseinitiating DSS, caused a significant increase in IFN-c, IL-17, and MPO release (Fig. 3 grey bars). Suboptimal DSS treatment in combination with fried commercial potato feeding raised levels of cytokine—as well as MPO secretion even further (Fig. 3 black bars). Consumption of high-GA potatoes in addition to DSS treatment further increased levels of all cytokines (Fig. 4). MPO levels were not further augmented by the higher GA contents in non-commercial potatoes; indeed, DSS-induced colitis mice fed fried high-GA potato skins did not demonstrate increased MPO activity above that seen in control DSS-induced colitis mice fed standard mouse chow (Fig. 4). Feeding of either fried commercial potato skins or highGA potato skins had similar effects on an inflammatory response in the cecum with regard to cytokine levels to those described for the colon. On the contrary, the feeding of fried potatoes was not effective in raising cytokine or MPO levels in the jejunum of DSS-treated mice and had only little effect in the ileum (data not shown). Small-Intestinal and Colonic Permeability Neither DSS treatment alone nor any tested potato-feeding regime (consumption of commercial potatoes alone or in conjunction with DSS treatment or consumption of highGA potatoes in conjunction with DSS treatment) instigated an increase in urinary lactulose/mannitol ratio above control mouse level, suggesting that the small-intestinal integrity was not compromised (data not shown). Conversely, colonic permeability, as measured by urinary sucralose excretion, was markedly increased in mice fed fried potato skins. In the absence of DSS treatment, consumption of fried commercial potatoes significantly increased sucralose in urine. While DSS treatment alone only marginally raised sucralose levels, in conjunction with commercial potato consumption, sucralose levels were significantly higher than control levels. In mice fed highGA potato skins, sucralose levels were significantly higher than in mice that were treated with standard chow alone or DSS alone (Fig. 5). Body Weight Body weight was significantly decreased over time in DSStreated mice fed fried high-GA potato skins when compared to control DSS-induced colitis mice fed standard
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Fig. 3 Mucosal colonic cytokine and myeloperoxidase levels following commercial potato feeding. Graphs represent IFN-c (a), IL-17 (b), TNF-a (c), and MPO levels from DSS-induced colitis mice fed fried commercial potato skins (solid bar) or standard mouse chow (hatched bars), and non-DSS-treated control mice fed potato skins (solid grey bars) or standard mouse chow (open bars). Feeding fried potatoes increased colonic cytokine levels. Values represent mean ± SEM. n = 6–10 mice per group. (*) Compared to untreated control mice fed standard mouse chow (p \ 0.05), # compared to DSS-induced colitis mice fed standard mouse chow (p \ 0.05)
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Fig. 5 Colonic permeability from mice following commercial potato feeding (a) and high-GA potato feeding (b). Graphs represent urinary sucralose secretion from DSS-induced colitis mice fed fried potato skins (solid bar), or standard mouse chow (hatched bars), mice fed potato skins in the absence of DSS (solid grey bars), and untreated control mice fed standard mouse chow (open bar). Feeding fried potatoes significantly increased colonic permeability. Values represent mean ± SEM. n = 6–10 mice per group. (*) Compared to non-DSS-treated controls fed standard mouse chow (p \ 0.05). # Compared to DSS-induced colitis mice fed high GA potato skins (p \ 0.05)
Fig. 4 Mucosal colonic cytokine and myeloperoxidase levels following high-GA potato feeding. Graphs represent IFN-c (a), IL-17 (b), TNF-a (c), and MPO levels from DSS-induced colitis mice fed fried high-GA potato skins (solid bar) or standard mouse chow (hatched bar), and from non-DSS-treated control mice fed standard mouse chow (open bar). Feeding high-GA fried potatoes significantly increased colonic cytokine levels but did not increase myeloperoxidase levels. Values represent mean ± SEM. n = 6–7 mice per group. (*) Compared to untreated control mice fed standard mouse chow (p \ 0.05)
mouse chow (Fig. 6). A similar loss in body weight was recorded in mice that were fed fried commercial potatoes independent of whether these mice were treated in addition with DSS or not (data not shown).
Discussion The current study aimed to investigate the effect of oral feeding of naturally occurring glycoalkaloids found in potatoes on models of IBD. Interestingly, epidemiologically
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Fig. 6 Daily body weight in DSS-induced colitis mice fed fried highGA potato skins (solid squares), standard mouse chow (circles) or untreated control mice fed standard mouse chow (triangles). Feeding fried potatoes resulted in significant weight loss. Values represent mean ± SEM. n = 6 mice per group. (*) Compared to untreated control mice fed standard mouse chow (p \ 0.05)
IBD has its highest prevalence in developed countries, and it is those same countries that have an increased consumption of fried potato skin products known to contain high levels of glycoalkaloids [5]. The relevance of glycoalkaloids to the pathogenesis of IBD may relate to the ability of these sterol agents to imbed into, disrupt, and permeabilize membrane bilayers [17]. As a consequence of this glycoalkaloid membrane disruption, exposure of the mucosal immune system, in genetically susceptible individuals, could result in the initiation of an inflammatory reaction that would not be contained. Glycoalkaloid levels in potatoes are carefully regulated, however, processing and handling methods can raise glycoalkaloid levels and thus pose health risks. While peeling or boiling reduces active glycoalkaloid levels, it is known that glycoalkaloids are stable during cooking in oil up to 180°C [13]. In addition, glycoalkaloids diffuse and accumulate in the surrounding frying oil causing further concentration in subsequent batches [18]. Indeed our data demonstrated that the total glycoalkaloid concentration in commercially purchased potatoes could be raised to almost threefold with just 12 min of frying in oil (Fig. 1). This increase amounted to more than double the regulated safe limit of 20 mg glycoalkaloid/100 g potato weight [14]. This could be cause for concern since potato glycoalkaloid levels are not regulated post-processing [13]. Feeding these commercial fried potato skins to IL-10 gene-deficient mice did not result in a measurable change in small-intestinal or colonic permeability. However, an increased cytokine-mediated inflammatory response (Fig. 3) was observed in the ileum, a region of these mice
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that is generally free of injury and inflammation. While this level of potato glycoalkaloid ingestion is able to induce intestinal inflammation, it may not be sufficient to enhance epithelial permeability, which is generally high in both the small and large bowel in IL-10 gene-deficient mice. However, we cannot exclude a mechanism of action independent of enhanced permeability for the injury in this model. A second animal model of IBD was utilized to gain additional insight into the effects of potato glycoalkaloids on the intestine and IBD. The same batch of potatoes that caused small-intestinal inflammation in IL-10 gene-deficient mice initiated enhanced secretion of inflammatory cytokines and MPO together with increased permeability in the colon of mice treated concomitantly with suboptimal doses of the colitogenic agent DSS. In fact, even in the absence of DSStreatment potato-fed wild-type mice demonstrated significantly elevated levels of cytokines. Utilizing high-GA fried potatoes instead of commercial potatoes intensified the inflammatory response in DSS-treated mice with increased colonic permeability and mucosal cytokine levels and subsequently worsened symptoms of body weight loss. In contrast, small-intestinal integrity was not compromised in these mice, with no change in inflammatory small-intestinal cytokine levels observed. It is intriguing to consider that the feeding of the fried potato skins, with their high glycoalkaloid levels, resulted in a defect of specifically colonic permeability that in turn exposed the mucosal immune compartment to luminal microbial contents, leading to the subsequent colonic inflammatory response. In these experiments it is not possible to determine if the permeability defect occurred as a primary event or a secondary event as a consequence of the inflammation. The fact that there is no small-intestinal permeability defect in the fried potato skin fed DSS-induced colitis model could imply that the permeability defect might have occurred secondarily. Previous in vitro studies have shown that glycoalkaloids induce caspase-3-dependent apoptosis in HT-29 cells in a time- and concentration-dependent manner [19]. While other recent studies observed the expression of apoptotic genes upon exposure to glycoalkaloids [20], treatment with different a-chaconine: a-solanine mixtures induced specific gene expression of polo-like kinase 3 (PIk3) in Caco-2 cells, a NF-jB downstream target that induces apoptosis. These treatments also increased the expression of cyclindependent kinase inhibitor 1A (CDKN1A), which retards cyclin-dependent progression through the cell cycle, leading to arrest at the G1 or G2/m phase [20]. Potentially, glycoalkaloids may promote epithelial damage by also reducing the number of dividing epithelial cells. Unlike mice fed high-GA potatoes, MPO was found significantly elevated in the colons of DSS-treated mice fed
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commercial potatoes. Since IFN-c is a potent chemoattractant of neutrophils, these elevated MPO levels can be explained by increased IFN-c after treatment with commercial potatoes but not high-GA potatoes [21]. Although both commercial and high-GA potatoes significantly increased IFN-c levels compared to controls MPO levels were low in mice fed high-GA potatoes. The reason for this discrepancy is only speculative, and may involve a feedback mechanism as a result of toxic doses of GA, causing a reduction in function and/or infiltration of MPO-producing neutrophils. Most recorded toxic effects of glycoalkaloids come from acute administrations [22]. In an ascending dose study, an individual fed 1.25 mg total glycoalkaloids/kg body weight became nauseous and vomited 4 h post-treatment. It is reasonable to conclude that cell disruption was responsible for these symptoms and that doses much smaller than 3 mg/ kg are able to elicit toxic effects [23]. a-Chaconine has an average half-life in the serum of about 44 h, therefore, chronic consumption of glycoalkaloid-containing foods could raise serum levels to toxic levels and have damaging effects on other organ systems such as the liver [23]. While we cannot completely exclude the possibility that compounds other than glycoalkaloids are responsible for the intestinal inflammatory response in our mice, we consider this unlikely. Presently, no other active agent is known that accumulates in potato skins to excessive amounts following frying and that could have an inflammatory effect on intestinal tissue. In addition, our results are in essence consistent with a previously published observation of enhanced inflammatory response in IL-10 gene-deficient mice following feeding with pure glycoalkaloid. The current study demonstrates that oral ingestion of naturally occurring glycoalkaloids from both commercial and high-GA potatoes worsens the intestinal injury associated with two IBD models. The role of glycoalkaloids as an environmental aggravator of IBD needs to be investigated further. Acknowledgments Canada (CCFC).
Funding
Crohn’s and Colitis Foundation of
References 1. Chichlowski M, Hale LP. Bacterial-mucosal interactions in inflammatory bowel disease—an alliance gone bad. Am J Physiol Gastrointest Liver Physiol. 2008;295:G1139–G1149. 2. Madsen KL, Malfair D, Gray D, et al. Interleukin-10 gene-deficient mice develop a primary intestinal permeability defect in response to enteric microflora. Inflamm Bowel Dis. 1999;5(4): 262–270. 3. Berg DJ, Zhang J, Weinstock JV, et al. Rapid development of colitis in NSAID-treated IL-10-deficient mice. Gastroenterology. 2002;123:1527–1542.
3085 4. Strober W, Fuss I, Mannon P. The fundamental basis of inflammatory bowel disease. J Clin Invest. 2007;117(3):514–521. 5. Smith DB, Roddick GJ, Jones JL. Potato glycoalkaloids: some unanswered questions. Trends Food Sci Technol. 1996;7:126–131. 6. Roddick JG, Weissenberg M, Leonard AL. Membrane disruption and enzyme inhibition by naturally-occurring and modified chacotriose-containing solanum steroidal glycoalkaloids. Phytochemistry. 2001;56(6):603–610. 7. Mandimika T, Baykus H, Vissers Y, et al. Differential gene expression in intestinal epithelial cells induced by single and mixtures of potato glycoalkaloids. J Agric Food Chem. 2007; 55(24):10055–10066. 8. Keukens EA, de Vrije T, van den Boom C, et al. Molecular basis of glycoalkaloid induced membrane disruption. Biochim Biophys Acta. 1995;1240(2):216–228. 9. Patel B, Schutte R, Sporns P, et al. Potato glycoalkaloids adversely affect intestinal permeability and aggravate inflammatory bowel disease. Inflamm Bowel Dis. 2002;8(5):340–346. 10. Egger B, Bajaj-Elliott M, MacDonald TT, et al. Characterization of acute murine dextran sodium sulphate colitis: cytokine profile and dose dependency. Digestion. 2000;62(4):240–248. 11. Dieleman LA, Palmen MJ, Akol H, et al. Chronic experimental colitis induced by dextran sulphate sodium (DSS) is characterized by Th1 and Th2 cytokines. Clin Exp Immunol. 1998;114(3): p385–p391. 12. Ku¨hn R, Lo¨hler J, Rennick D, et al. Interleukin-10-deficient mice develop chronic enterocolitis. Cell. 1993;75:263–274. 13. Friedman M. Potato glycoalkaloids and metabolites: roles in the plant and in the diet. J Agric Food Chem. 2006;54(23):8655– 8681. 14. AOAC International. AOAC official methods of analysis. AOAC official method 997.13. Glycoalkaloids (a-solanine and a-chaconine) in potato tubers. In: Trucksess MW, ed. Natural Toxins. Gaithersburg: AOAC; 1997:63–65. 15. Meddings JB, Gibbons I. Discrimination of site-specific alterations in gastrointestinal permeability in the rat. Gastroenterology. 1998;114(1):83–92. 16. Sydora BC, Tavernini MM, Doyle JS, et al. Association with selected bacteria does not cause enterocolitis in IL-10 genedeficient mice despite a systemic immune response. Dig Dis Sci. 2005;50:905–913. 17. Keukens EA, de Vrije T, Fabrie CH, et al. Dual specificity of sterol-mediated glycoalkaloid induced membrane disruption. Biochim Biophys Acta. 1992;1110(2):127–136. 18. Sinden SL, Webb RE. Effect of variety and location on the glycoalkaloid content of potatoes. Am J Potato Res. 1972; 49(9):334–338. 19. Yang SA, Paek SH, Kozukue N, et al. Alpha-chaconine, a potato glycoalkaloid, induces apoptosis of HT-29 human colon cancer cells through caspase-3 activation and inhibition of ERK 1/2 phosphorylation. Food Chem Toxicol. 2006;44(6):839–846. 20. Mandimika T, Baykus H, Vissers Y, et al. Differential gene expression in intestinal epithelial cells induced by single and mixtures of potato glycoalkaloids. J Agric Food Chem. 2007;55(24):10055–10066. 21. Ribeiro RA, Cunha FQ, Ferreira SH. Recombinant gamma interferon causes neutrophil migration mediated by the release of a macrophage neutrophil chemotactic factor. Int J Exp Pathol. 1990;71(5):717–725. 22. Kozukue N, Yoon KS, Byun GI, et al. Distribution of glycoalkaloids in potato tubers of 59 accessions of two wild and five cultivated solanum species. J Agric Food Chem. 2008;56(24): 11920–11928. 23. Mensinga TT, Sips AJ, Rompelberg CJ, et al. Potato glycoalkaloids and adverse effects in humans: an ascending dose study. Regul Toxicol Pharmacol. 2005;41(1):66–72.
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