Modification of American Institute of Nutrition Rat Diet in Mammary Cancer Research

This research was performed to test the effect of date palm fruit (Phoenix datylifera L.) of (Al-Barhi) type at the two maturity stages “Rutab” and “Tamr” on the 7,12-dimethylbenz(α)anthracene (DMBA)-induced mammary cancer using the rat model. The experimental diets included soybean group as a control group since soybean is known to be protective against mammary cancer. The diets, except for the soybean diet, were a modification of the American Institute of Nutrition-1993 (AIN-93) diet that is free of any soybean products. Soybean oil was replaced by a mixture of canola and sunflower oils in amounts that give ratios of ω-6:ω-3 fatty acids and PUFA:SFA similar to those of the AIN-93 diet which are based on soybean oil namely 7.5:1.0 and 4.0:1.0 respectively. It is concluded that in DMBA-induced mammary cancer experiments, a mixture of canola and sunflower oils in a ratio of 0.6:1.0 (v/v) canola oil:sunflower oil would replace soybean oil.


Introduction
Mammary cancer is a neoplastic change in the epithelial cells of the mammary tissue (Hieger, 1961).The use of humans in experimental cancer research is not ethical.This makes the use of animal models for the study of mammary cancer more practical.The use of 7,12-Dimethylbenz(α)anthracene (DMBA) to induce mammary cancer in rodents, is one of the most two commonly used models to study mammary cancer (Guzman et al., 1999).
Several studies examined the antioxidant power of various extracts of the date palm fruit (Qusti et al., 2010;Khanavi et al, 2010).According to the available literature, no study had examined the effect of the whole date palm fruit on mammary cancer in vivo.Thus, an experiment was performed to test the effect of date palm fruit (Phoenix datylifera L.) of (Al-Barhi) type at the two maturity stages "Rutab" (freeze-dried) and "Tamr" on the 7,12-dimethylbenz(α)anthracene (DMBA)-induced cancer using the rat model.
The American Institute of Nutrition-1993 (AIN-93) recommends the use of soybean oil as the source of fatty acids for growing rats.On the other hand, soybean oil and soy protein isolate were found to be protective against DMBA-induced mammary cancer (Rogers, 1997;Hakkak et al., 2000).This necessitated the replacement of soybean oil with another type of oil which contains similar amounts of fatty acids present in soybean oil.

Materials
Test meals which were fed to the animals were prepared in such a way to be isocaloric and isonitrogenous according to the guidelines of the American Institute of Nutrition (1993) for growing animals (AIN-93G) recommended by Reeves (1997) with modification of the type of oil used.
University of Jordan in compliance with the standards of the Deanship of Academic Research.

Methods
The diets which were fed to the experimental animals were prepared according to the AIN-93 guidelines with the following modifications: 1) The soybean oil has been replaced by a mixture of canola and sunflower oils in such away to get ratios of linoleic acid (LA):α-linolenic acid (ALA) and polyunsaturated fatty acids (PUFAs):saturated fatty acids (SFAs) similar to those in soybean oil as recommended by AIN-93.
2) Powdered soy bean seeds, freeze-dried "Rutab", and "Tamr" were added at the level of 30% of the diet mixture weight with completion of macronutrient contents to the recommended weights and correction of the weight of starch, casein, and cellulose (Al-Sayyed et al., 2013) according to the proximate composition of the plant products shown in Table 1.Experiments on mammary cancer using freeze-dried "Rutab" and "Tamr" were based on AIN-93 diet and compared with soybean as control (Al-Sayyed, et al., 2013).Four meals were used in the experiment as follows: AIN-93G, AIN-93G containing soybean seeds (AIN-93G+Soybean), AIN-93G containing freeze dried "Rutab" (AIN-93G+"Rutab"), and AIN-93G containing "Tamr" (AIN-93G+"Tamr").Since soybean oil was not used in the dates experimental groups, trials were done to obtain the optimum oil characteristics similar to those of soybean oil recommended by AIN-93.

Results
The LA, ALA, PUFA, SFA contents and their ratios in soybean, canola, and sunflower oils are shown in Table 2.Many trials were done to get similar ratios to soybean oil (Table 3).The results of the study were published elsewhere (Al-Sayyed et al. 2013, 2014a, 2014b).

Table 1 .
Proximate composition of soybean and date fruits used in the experiment 1

100g raw soybean seeds) Fresh "Rutab" Freeze-dried "Rutab" 4 "Tamr" Stage
Note.1Results are average values of duplicate samples; 2 Protein content was calculated by multiplication of nitrogen content by a factor of 6.25 for date palm fruit and 7.2 for soybean according to Holland et al. (1995); 3 Carbohydrate content was calculated by difference; 4 Calculated values (except for moisture content); 5 Energy (Kcal.) (calculated by multiplying the carbohydrate and protein contents by 4 and the fat content by 9).