The Development of Diets to Induce Atherogenic Lipid Profiles for Cynomolgus Monkeys in Their Country of Origin

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Table 1. Composition of the experimental diets

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Table 2. Nutrient composition of all atherogenic diets

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2.1. Diet Analyses

All diets were analyzed for their macronutrient composition following the procedures AOAC ^[2] and total energy by using bomb calorimeter. Cholesterol was measured by spectrophotometer by using enzymatic procedures. The nutrient compositions showed in Table 2.

2.2. Body Weight Assessments

Body weight, waist circumference and trunk length were recorded on all monkeys monthly. Before measurements they were anesthetized with ketamine HCl (10-12 mg/kg, given intramuscular).

a. Body weight (kg) – weight to the nearest gram

b. Waist circumference (cm) - A flexible tape measure was placed around the monkey’s abdomen at the level of the umbilicus to measure waist circumference (cm). The measurements were always made in duplicate.

c. Trunk length (cm) – Measure the distance (cm) from the supra-sternal notch to the pubic symphysis, using calipers or non-flexible ruler and made by duplicate measurements. The data were convert from cm to meters.

d. The adiposity index was calculated as the (g) of body weight/ divided by (cm) distance from the supra-sternal notch to the symphysis pubis.

2.3. Nutrient Absorption

Food consumption was measured everyday by recording the weight of food fed to each animal (g) minus with the weight of food remaining after 24 hours. Dry matter food was measured by placing the food in a drying oven 105C for 8 hours. Nutrient consumptions were calculated by multiplying dry matter intake by nutrient concentration of the diet (macro nutrients and fatty acids). Feces were collected using metabolic cages during the last seven days of the experiment. Ten percent of daily total fecal production from each animal was saved and frozen for proximate analysis. To evaluate the quality of diet and nutrient absorption, the nutrient in the feces was subtracted from nutrient consumption ^[6].

2.4. Plasma Lipid Measurements

Blood samples for plasma lipid measurements were collected by femoral venipuncture using standard techniques while the monkeys were sedated by Ketamine. Whole blood was centrifuged in order to get plasma and the lipid profiles were determined using a spectrophotometer (need more methods here – machine name etc.).

2.5. Statistics

The study used a randomized parallel arm design to allocate the monkeys to the four dietary groups.. All data are reported as mean ± standard deviation. The data were analyzed using ANOVA comparing differences in the clinical measurements among the monkeys in the experimental diet groups. Duncan multiple range test was used. All statistical analyses were done using SPSS version 6 program.

3. Result

3.1. Baseline Characteristics

All animals adapted well to the IPB-1 diet during three months baseline (pre randomization) observations. Presented in Table 3 are the baseline data for all 24 monkeys. As expected from our previous study, the IPB-1 diet resulted in hypercholesterolemia while maintaining normal body weights and adipose index. There was considerable individual variation in the degree of hypercholesterolemia and food consumption as evidence by the rather high standard errors.

3.2. Diet Effects on Morphometric Measures

Morphometric measures of monkeys fed the original IPB-1 diet and the four modified diets are presented in a Table 4. There were no significant differences found among any of the diet groups compared to one another or change from baseline.

Table 3. Baseline study of monkeys after being fed IPB1 diet for 3 months

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Table 4. Monthly body morphometric on the monkeys fed experimental diets

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3.3. Diet Effects on Nutrient Intake

All four of the diets were palatable and food consumption was as expected. The average food consumption during the three months adaptation period was 136 g animal^-1 day^-1 and there were no increases or decreases after the monkeys were switched to the experimental diets. Food consumption averaged 139 g animal^-1 day^-1during twelve months of observation. The nutrient (protein, fat and carbohydrate) consumption was essentially the same for all four diet groups (Table 5).

The percentage of dry matter, protein, fat and carbohydrate absorption was similar for all four diet groups (Table 5). Generally, all of the diets had good digestibility values and were absorbed well.

Table 5. Nutrient consumption and absorption (%) by cynomolgus monkeys fed experimental diets

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3.4. Diet Effects on Plasma Lipids and Lipoproteins

The IPB 1+CO diet, the IPB 1+CO+PM diet and the IPB 1+CO+CC induced a similar atherogenic plasma lipid profile, with marked increases in total plasma cholesterol concentrations and decreases in high density lipoprotein cholesterol concentrations (Table 6). The failure of the IPB 1+CO+PEY, prepared with dried egg yolk, to induce an atherogenic plasma lipid profile is unexplained. The experience at the Wake Forest Primate Center has been that if diets are made equivalent in cholesterol concentration there are no consistent or significant differences in the induction of an atherogenic lipid profile between crystalline cholesterol and the cholesterol contained in powdered egg yolk.

Table 6. Plasma lipid profile of cynomolgus monkey fed experimental diets during 12 months

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