This is the first study in which a comparison is made between the ability of different berry types to influence chemically induced tumor development in an animal model system. The rat esophagus tumor model is particularly useful for making this comparison because the provision of berry powder in the diet ad libitum
permits the localized absorption of berry compounds directly into the esophagus on a consistent basis. This is especially relevant for the anthocyanins and ellagitannins in berries because the uptake of these compounds into blood is generally less than 1% of the administered dose (34
). Therefore, the localized absorption of these compounds is thought to be important for their chemopreventive potential (36
Our results indicate that all seven berry types were effective in reducing esophageal tumor incidence and multiplicity when administered in the diet in a post-initiation protocol. This is important because this protocol permits an evaluation of whether the berries are capable of preventing the progression of NMBA-induced premalignant lesions (dysplastic lesions) to papillomas (6
). This has relevance to the human situation in which chemopreventive agents are evaluated for their ability to inhibit the progression of dysplastic lesions in the esophagus (identified by endoscopy) to squamous cell carcinoma (22
). The berry types were not significantly different in their ability to prevent esophageal tumorigenesis in this protocol; however, the data are preliminary in that the berries were tested at only a single dose level (5%) in the diet. The reason for selection of a 5% berry diet is that this dose level of BRBs has consistently produced an inhibitory effect on NMBA-tumorigenesis in the rat esophagus in multiple studies (4
). Higher dose levels (10% and 20%) do not produce significantly greater inhibitory effects than the 5% BRB diet, and, at 2.5% of the diet, BRBs were not effective (data not published). It is conceivable, however, that differences in the ability of the various berry types to prevent esophageal tumorigenesis could be revealed if they were tested at doses that are both higher and lower than 5% of the diet.
The ellagitannins and anthocyanins in berries have been shown in multiple studies to produce chemopreventive effects in vitro
and in vivo
). In 1990, we reported that dietary ellagic acid, the chemopreventive component of the ellagitannins, inhibits NMBA-induced tumorigenesis in the rat esophagus (23
). Recently, we reported that an anthocyanin-enriched fraction of BRBs was equally as effective as whole BRB powder itself in reducing NMBA-tumorigenesis in the rat esophagus (4
). We predicted, therefore, that those berry types with high levels of anthocyanins and ellagitannins might be the most effective in inhibiting NMBA-tumorigenesis in the esophagus. Results from the present study suggest that this is not the case, at least when the berries are provided at 5% of the diet. In fact, the present results confirm a previous report from our laboratory in which STRWs were found to be nearly as effective as BRBs in preventing rat esophageal tumorigenesis, even though STRWs have lower levels of both anthocyanins and ellagitannins (13
) (). This is the first report of the ability of red raspberries (RRBs) to inhibit NMBA-induced tumorigenesis in the rat esophagus, and they appear to be quite effective. For comparative purposes, RRBs were obtained from growers in Ohio and Washington, and berries from both states appear to be about equally effective in preventing esophageal tumor progression. To our knowledge, this is the first attempt to compare the same berry type grown in different regions of the United States for its ability to inhibit tumorigenesis in vivo
. Blueberries are also effective, and they have high levels of anthocyanins and very low levels of ellagitannins (26
) (). These results suggest, therefore, that additional studies of the chemopreventive potential of commercially produced strawberry, red raspberry and blueberry powders in preclinical animal model systems (and ultimately in humans) are warranted and desirable in that these berry types are readily available for consumption throughout the entire year.
Because of their recent popularity, and varying levels of anthocyanins and ellagitannins, we examined three “exotic” berries—wolfberry, noni and açaí—for their ability to inhibit tumor progression in the rat esophagus. Wolfberry contains some ellagitannins and low levels of anthocyanins; however, the inhibitory effect of these berries against esophageal cancer could well be due to their high level of carotenoids (31
). Zeaxanthin, an antioxidant, is the most abundant carotenoid in wolfberry, and a human trial showed that the dietary intake of wolfberry increased plasma levels of zeaxanthin (37
). In addition, as mentioned above, in sarcoma cell (S180) tumor-bearing mice, a wolfberry-derived polysaccharide-protein complex reduced tumor weight and increased interleukin-2 (IL-2) expression (21
). Although the macromolecular structure of wolfberry polysaccharides has not been elucidated, preliminary structural studies indicate that they exist in the form of complex glycoconjugates (38
). The chemopreventive effect of noni is likely due to a number of chemical constituents that exhibit strong antioxidant activity, including certain anthraquinones, flavonol glycosides, iridoid glycosides and triterpenoids (16
). To our knowledge, anthocyanins and ellagitannins have not been detected in noni. Noni has been shown to inhibit tumor development and induce apoptosis of Ehrlich ascites tumors in Balb-c mice (39
), and, as mentioned above, noni fruit glycosides suppress TPA- and EGF-induced transformation of mouse epidermal JB6 cells, an effect associated with reduced AP-1 expression (18
Freeze-dried açaí fruit pulp and skin has been shown to contain about 3.19 mg/g of anthocyanins, principally cyanidin-3-glucoside and cyanidin-3-rutinoside (40
). However, the anthocyanins are thought to contribute a relatively small percentage of the total antioxidant capacity of açaí fruit because açaí also contains appreciable quantities of proanthocyanidins (12.89 mg/g), which undoubtedly contribute substantially to their antioxidant potential (32
). It seems likely that the anthocyanins and proanthocyanidins are responsible for at least a portion of the chemo-preventive activity of açaí in the present study. To our knowledge, there are no reports of the presence of ellagitannins in açaí.
The present study suggests that another mechanism by which berries inhibit NMBA-induced esophageal tumorigenesis is through the regulation of cytokine expression. All berry types reduced the levels of IL-5 and GRO/KC in the serum of NMBA-treated rats. Elevated expression of IL-5 and other interleukins has been reported in rat lung adenocarcinomas induced by N
). GRO/KC is the rat analog for human Interleukin-8 (IL-8), and human IL-8 is a macrophage-derived mediator of angiogenesis (42
). The ability of all berry types to reduce serum levels of IL-5 and GRO/KC may therefore be related to their inhibitory effect on NMBA-induced esophageal tumorigenesis. The BRB and açaí diets significantly upregulated serum levels of IFNγ and activated macrophage-released IFNγ induced apoptosis through the Fas/FasL pathway in glioma cells (43
). Thus, it is possible that these two berry types influence the apoptotic rate in NMBA-treated rat esophagus as a mechanism of tumor inhibition. These observations on serum cytokine levels require confirmation in NMBA- and berry-treated esophageal tissues to determine if the changes in serum levels reflect tissue levels of these cytokines.