Yvonne V. Yuan

Effect of casein, casein phosphopeptides and calcium intake on ileal 45Ca disappearance and temporal systolic blood pressure in spontaneously hypertensive rats

Paracellular 45Ca absorption and temporal systolic blood pressure (SBP) measurements were recorded in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats fed on casein (C) and soya-bean-protein isolate (S) diets, containing 20 (H), 5 (H) and 0.5 (L) g Ca/kg. Similar measurements were also taken in SHR rats only fed on C-M and S-M diets supplemented with 30 g caseinophosphopeptides (CPP)/kg. Absorption of 45Ca from the ileal loop was equivalent in both SHR and WKY animals and largely affected by the level of dietary Ca. In addition, animals fed on C diets exhibited significantly (P < 0.05) greater ileal absorption of 45Ca compared with S-fed animals. This result was attributed to the presence of CPP and a greater (P < 0.05) proportion of soluble 45Ca in the contents of the ileum. Animals fed on S diets supplemented with CPP confirmed this finding. The SBP of SHR rats was higher (P < 0.01) than WKY controls after 9-10 weeks of age. The temporal pattern of observed hypertension was independent of dietary influence in the SHR. The severity of hypertension in SHR rats was affected only by dietary Ca deficiency, and not by Ca supplementation or CPP enhancement of Ca bioavailability. These findings suggest that tryptic digestion products of casein in milk can enhance Ca bioavailability by increasing Ca solubility; however, this action had no effect in reducing hypertension in SHR.

Caseinophosphopeptides and calcium biovailability

Abstract Bioactive peptides derived from the tryptic digestion of casein, known as caseinophosphopeptides (CPP), possess physicochemical properties that enable the chelation of various bi- and trivalent minerals, thereby enhancing mineral solubility in the lower small intestine. The significance of the interaction between CPP and calcium ions, in particular, for enhancing calcium absorption is presently a controversial issue due to the variations in the methodologies used to assess calcium biovailability.

Confirmation of calcium absorption and femoral utilization in spontaneously hypertensive rats fed casein phosphopeptide supplemented diets

Abstract Caseinophosphopeptides (CPP) have been shown to enhance calcium solubility and absorption from ligated segments of rat small intestine but there are few data in regard to the effect on calcium balance and utilization. This study evaluated the effect of supplementing casein and soy diets with CPP on FER, in situ paracellular calcium absorption, 24 hr calcium balance and mineralization in spontaneously hypertensive rats (SHR). Two principal phosphopeptides, α en -(1–21) and β-(1–25) casein were identified in the CPP by peptide sequencing following isolation by HPLC. Animals were fed 20% casein, and soy protein isolate diets, as well as casein and soy protein diets supplemented with 3% CPP. Animals fed CPP-soy protein diets exhibited an improved (P 45 Ca and absorption from the ligated loop were also significantly (P

Influence of dietary cholesterol and fat source on atherosclerosis in the Japanese quail ( Coturnix japonica )

The Japanese quail has been used as a model of human atherosclerosis to investigate the mechanisms underlying the development of vascular lesions, i.e. hyperlipoproteinaemia and impaired endogenous antioxidant status. In the present study, Japanese quail were fed on semi-purified diets containing butter, beef tallow or soyabean-oil blends, with either 0.5 or 5 g cholesterol/kg for 9 weeks to examine the effects of dietary fat blends varying in fatty acid composition and cholesterol intake on plasma lipids and aortic atherosclerotic plaque and sterol composition. These findings were related to possible diet-induced changes in antioxidant status of selected tissues. Hypercholesterolaemia was confirmed (P < 0.001) in birds fed on high-cholesterol (HC) diets. Plasma total cholesterol concentration and cholesterol content of lipoprotein fractions in hypercholesterolaemic birds were lower (P < 0.05) in quail fed on the soyabean-oil blend. Plasma triacylglycerol content was increased (P < 0.001) in HC-fed birds. Dietary fat blends did not influence plasma triacylglycerol levels. Tissue antioxidant status (catalase (EC 1.11.1.6), glutathione peroxidase (EC 1.11.1.9), glutathione reductase (EC 1.6.4.1) and superoxide dismutase (EC 1.15.1.1) activities and glutathione content) was generally not greatly affected by dietary fat blend or cholesterol treatment. Birds fed on HC diets exhibited severe (P < 0.001) atherosclerotic plaque in aortas which was not influenced by the source of dietary fat blend. Scanning electron microscopy confirmed results of visual aortic plaque scoring using dissecting light microscopy. Several cholesterol oxides were identified and quantified in aortic plaque from HC-fed birds (5,6 alpha-epoxy-5 alpha-cholesterol, 7(beta-hydroxycholesterol and 7-ketocholesterol) regardless of dietary fat blend. The results indicate that dietary fat blends varying in polyunsaturated:saturated fatty acid ratios only marginally influence the degree of hypercholesterolaemia in atherosclerosis-susceptible quail fed on atherogenic diets only, and are not a factor, compared with sterol feeding, in modulating the degree of atherosclerosis or the aortic oxysterol content in these same birds. Moreover, diet-induced hyperlipoproteinaemia had only a small effect on antioxidant status of selected tissues examined.

Calcium absorption and bone utilization in spontaneously hypertensive rats fed on native and heat-damaged casein and soya-bean protein

The effects of dietary protein on Ca bioavailability and utilization in bone were examined in male spontaneously hypertensive rats (SHR) fed on diets containing either casein (200 g/kg (control), 60 g/kg or heat-damaged (HD) 200 g/kg) or soya-bean protein isolate (200 g/kg (control), 60 g/kg, or HD 200 g/kg). Casein was heat-damaged to limit casein-phosphopeptide (CPP) production in order to evaluate casein enhancement of Ca bioavailability. All diets contained an adequate level of Ca (5 g/kg). A 24 h mineral balance study was performed when animals were 10 weeks old, followed by measurement of in situ paracellular Ca disappearance, femur mineralization and biomechanics at 14 weeks of age. Digestibility of soya-bean and both HD proteins estimated in vitro was reduced compared with native casein. Animals fed on HD and 60 g/kg protein diets exhibited decreased (P < 0.05) body weight gain, dry matter intake and feed efficiency compared with controls. The ileal disappearance of 45Ca was lower (P < 0.05) in animals fed on HD casein and all the soya-bean protein diets. Ca balance was not strongly affected by dietary treatments. A significant (P < 0.05) interaction between protein source and reduced protein intake was observed for femur calcification and physical measurements. Femur bending failure energy and biomechanical force measurements were reduced (P < 0.05) in HD and 60 g/kg casein and soya-bean protein fed animals. These findings suggest that whole-body Ca homeostatic mechanisms were involved in compensating for reduced Ca bioavailability and retention from casein diets modified to reduce protein digestibility and CPP production.

Casein phosphopeptides enhance paracellular calcium absorption but do not alter temporal blood pressure in normotensive rats

Abstract Casein phosphopeptides (CPP) were purified from an in vitro tryptic digestion of casein and used for in vitro calcium binding affinity experiments to determine the optimal binding characteristics of CPP. These studies were followed by animal feeding trials designed to examine the absorption of 45 Ca from the distal part of the small intestine. Male Wistar rats were meal-fed isonitrogenous diets containing casein, whey protein, soy protein isolate (SPI) or a milk protein concentrate (MPC) with adequate dietary calcium (0.7%) for a 10-week period. The absorption of 45 Ca was measured from the disappearance of 45 Ca from a ligated ileum loop. There were no differences in body weight gain or plasma Ca, Mg, K, Na and Ca +2 between animal groups fed the different protein sources. The 45 Ca absorption from the ileum was significantly (P 40 Ca was also significantly (P

Estimation of dietary calcium utilization in rats using a biomechanical functional test

Three-point bending of femora was evaluated as a biomechanical functional test of calcium utilization in male Wistar rats fed 20% casein and soy protein diets containing different levels of dietary calcium (2·0, 0·5 and 0·05% w/w), respectively. Rats were meal-fed for 10 weeks after which animals were sacrificed and both femora removed. Femur mineral composition and biomechanical parameters: bioyield, peak force, bending failure energy and a normalized force parameter, maximum bending stress were determined. Femur calcium content and ash weight were significantly (p < 0·05) decreased in animals fed low calcium diets compared to those fed medium and high calcium diets. Femur biomechanics were not related to animal growth parameters. Femur biomechanical parameters were correlated with dietary calcium intake and femur composition in both casein- and soy-fed animals. The bioyield and peak force parameters identified were significantly (p < 0·001) correlated with femur calcium content in casein- and soyfed rats. Calcium utilization was indicated by regression equations relating bone calcium content and ash weight to bioyield and peak force, respectively, for casein- and soy-fed animals. Bending failure energy could not be reliably modelled using these same variables, suggesting that it is influenced by not only bone mineralization but possibly also the collagen matrix component. These results indicate that three-point bending can be useful in assessing calcium utilization from the diet. Bone biomechanics were not influenced by casein and soy dietary protein sources.

Paracellular calcium absorption, femur mineralization and biomechanics in rats fed selected dietary proteins☆

Abstract The absorption of 45Ca from the distal section of the lower small intestine, and its subsequent deposition in the femur were examined in male Wistar rats fed diets containing 20% casein (C), whey protein (W), a milk protein concentrate (MPC), and a soy protein isolate (SPI), respectively. These experiments were performed along with in-vitro studies designed to estimate the relative digestibilities of the dietary protein sources. In the animal experiments, all diets contained an adequate calcium level (0·7%). Individual rats were meal-fed for 10 weeks, after which calcium absorption was measured from the disappearance of 45Ca from the ligated ileal loop; as well, femoral deposition of 45Ca and mineral composition were examined. Estimates of calcium utilization were made from femur and tibia biomechanical measurements. A markedly lower digestibility of the soy and whey proteins was observed compared to the casein and milk protein concentrate sources, respectively. There were no differences in the daily body weight gain, and plasma calcium levels. The absorption of 45Ca from the ileum was significantly (p = 0·043) lower in SPI-fed rats, compared to C-, W- and MPC-fed animals. There was no treatment effect on femoral 45Ca deposition, total Ca, Mg or Ca/PO4 ratio. A significant correlation between femur calcium content and bone strength was determined; however, there was no treatment effect on either femur or tibia biomechanical properties. These results indicate a similar utilization of calcium in animals fed dietary proteins that may differ in digestibility.

Influence of increased saturated fatty acid intake from beef tallow on antioxidant status and plasma lipids in atherosclerosis-susceptible Japanese quail

Abstract In this study, the relationship between tissue antioxidant status and atherogenesis was examined using the atherosclerosis-susceptible Japanese quail model. Male Japanese quail were fed commercial poultry diets containing two levels of beef tallow (i.e. 6.0 or 12.0% ww) that were balanced for endogenous cholesterol (i.e. 0.05% ww) or supplemented to a high level of cholesterol (i.e. 0.5%), for 9 weeks to examine the effects of increased SFA and cholesterol intake on plasma lipids, tissue antioxidant status and atherosclerotic plaque development in quail. Diets containing 12% beef tallow resulted in lower diet 18:2n-614:0 fatty acid ratios. Hypercholesterolemia ( P P P P P = 0.002) in birds fed high cholesterol diets. Differences in susceptibility to oxidative challenge with H 2 O 2 were observed in heart and liver tissue. Forced production of lipid peroxidation, as measured by tissue thiobarbituric reactive substances (TBARS), was lower ( P

The Effect of Lactose and Fermentation Products on Paracellular Calcium Absorption and Femur Biomechanics in Rats

Abstract The paracellular absorption and subsequent utilization of calcium was examined in male Wistar rats fed diets containing a skim milk protein concentrate (SMPC), SMPCxa0+xa020% lactose (ML) SMPCxa0+xa050% lactose (HL) and yogurt powder concentrate (Y), respectively. Animals fed the HL diet exhibited a lower (pxa0≤xa00.05) food intake resulting in decreased calcium intake and body weight gain to SMPC, ML and Y fed animals. Plasma α-amino nitrogen and triglyceride levels were significantly (pxa0≤xa00.05) lower in HL fed animals than SMPC and ML fed animals, indicating nutrient malabsorption in these animals. Intestinal absorption and femur deposition of 45 Ca were not different in SMPC, ML and Y fed animals, but significantly (pxa0≤xa00.05) enhanced in HL fed animals. Femur ash weight and mineral composition were not affected by dietary treatment, but femur weight and biomechanical bone hardness were significantly (pxa0≤xa00.05) lower in HL fed animals. Our results indicate that lactose enhancement of calcium absorption occurs at a critical intestinal concentration of lactose and is not seen when substituted with lactose fermentation products. There was no evidence indicating a difference between calcium bioavailability from milk and yogurt dairy sources. The reduced bone strength in HL fed animals could not be attributed to reduced femur mineralization. A greater effect associated with other forms of nutrient malabsorption is suspected.