Anne Blais

Colon luminal content and epithelial cell morphology are markedly modified in rats fed with a high-protein diet

Hyperproteic diets are used in human nutrition to obtain body weight reduction. Although increased protein ingestion results in an increased transfer of proteins from the small to the large intestine, there is little information on the consequences of the use of such diets on the composition of large intestine content and on epithelial cell morphology and metabolism. Rats were fed for 15 days with either a normoproteic (NP, 14% protein) or a hyperproteic isocaloric diet (HP, 53% protein), and absorptive colonocytes were observed by electron microscopy or isolated for enzyme activity studies. The colonic luminal content was recovered for biochemical analysis. Absorbing colonocytes were characterized by a 1.7-fold reduction in the height of the brush-border membranes (P = 0.0001) after HP diet consumption when compared with NP. This coincided in the whole colon content of HP animals with a 1.8-fold higher mass content (P = 0.0020), a 2.2-fold higher water content (P = 0.0240), a 5.2-fold higher protease activity (P = 0.0104), a 5.5-fold higher ammonia content (P = 0.0008), and a more than twofold higher propionate, valerate, isobutyrate, and isovalerate content (P < 0.05). The basal oxygen consumption of colonocytes was similar in the NP and HP groups, but ammonia was found to provoke a dose-dependent decrease of oxygen consumption in the isolated absorbing colonocytes. The activity of glutamine synthetase (which condenses ammonia and glutamate) was found to be much higher in colonocytes than in small intestine enterocytes and was 1.6-fold higher (P = 0.0304) in colonocytes isolated from HP animals than NP. Glutaminase activity remained unchanged. Thus hyperproteic diet ingestion causes marked changes both in the luminal environment of colonocytes and in the characteristics of these cells, demonstrating that hyperproteic diet interferes with colonocyte metabolism and morphology. Possible causal relationships between energy metabolism, reduced height of colonocyte brush-border membranes, and reduced water absorption are discussed.

Bovine lactoferrin improves bone status of ovariectomized mice via immune function modulation

We have previously shown that bovine lactoferrin (bLF) supplementation can have a beneficial effect on postmenopausal bone loss by modulating bone formation and resorption. A direct effect of bLF on bone metabolism is support by its presence in mice blood. Moreover we know that LF plays a key role in innate immunity and recent studies have shown its ability to modulate adaptive immunity. In particular bLF ingestion prevents recruitment and activation of immune cells at inflammatory sites. We propose that LF through its ability to modulate maturation and differentiation of leucocytes can participate to abolish the deregulation induced by estrogen deficiency on T cells. This study evaluated the effects of bovine lactoferrin on immune function in ovariectomized mice. We investigated whether bLF ingestion could prevent bone loss via modulation of immune function. Three-month-old female C3H mice were either ovariectomized or sham-operated and fed for 1, 2 or 4 months with a control diet (AIN-93M) or the same diet including 10g bLF/kg diet. Bone mineral density was determined using a Lunar Piximus densitometer. The immune parameters were assessed by flow cytometry. In addition, Real-Time PCR was performed to quantify TNFα expression and plasma cytokines were measured at 4 months with Luminex. Ovariectomy induced significant changes on bone parameters and increased recruitment of macrophages, dendritic cells, and B and T cells associated with T lymphocyte activation in bone marrow. Compared to the control diet, ingestion of bLF-enriched diet for 2 months prevented T cell activation and restored dendritic and B cell populations in the bone micro-environment in ovariectomized mice. Furthermore, TNFα expression in bone was decreased by bLF supplementation after 2 and 4 months. Similarly, a decreased plasma level of TNFα was observed concomitantly to an increase of IL-10 level. In conclusion, these experiments suggest that bLF can mediate the prevention of lymphocyte activation and cytokine release in the bone micro-environment. Dietary bLF supplementation could have a beneficial effect on postmenopausal bone loss by modulating immune function.

Glycosylations of κ-Casein-Derived Caseinomacropeptide Reduce Its Accessibility to Endo- but Not Exointestinal Brush Border Membrane Peptidases

Caseinomacropeptide (CMP) is a peptide obtained from kappa-casein hydrolysis by gastric proteinases and which exhibits various biological activities. The aim of this study was to analyze the intestinal processing of CMP at the brush border membrane (BBM) level. Intestinal BBM vesicles (BBMV) were used to digest glycosylated and unglycosylated CMP. Our results demonstrated that whatever was the glycosylated state of CMP, they were digested by BBMV intestinal enzymes, from macropeptides to free amino acids. The digestion of unglycosylated and glycosylated CMP throughout the action of exopeptidases was similar, but the activity of endopeptideases on glycosylated CMP was limited, certainly due to the attached O-glycosylations. Consequently, much more peptides were identified from the unglycosylated than from the glycosylated CMP. In addition, the glycosylation core as well as the number of the attached glycosylated chain modified the kinetic of digestion; the most heavily glycosylated forms being the slowest digested.

Protein quality affects bone status during moderate protein restriction in growing mice.

Adequate protein intake during development is critical to ensure optimal bone gain and to attain a higher peak bone mass later on. We hypothesized that the quality of the dietary protein is of prime importance for bone physiology during moderate protein restriction. The target population was growing Balb/C mice. We compared two protein restricted diets (6% of total energy as protein), one based on soy (LP-SOY) and one based on casein (LP-CAS). For comparison, a normal protein soy-based control group (NP-SOY) and a low protein group receiving an anabolic daily parathyroid hormone (PTH) 1-34 injection (LP-SOY+PTH) were included in the protocol. After 8weeks, LP-SOY mice had reduced body weights related to a lower lean mass whereas LP-CAS mice were not different from the NP-SOY group. LP-SOY mice were characterized by lower femoral cortical thickness, bone volume, trabecular number and thickness and increased medullar adiposity when compared to both the LP-CAS and NP-SOY groups. However, the dietary intervention had no effect on the vertebral parameters. The negative effect of the LP-SOY diet was correlated to an impaired bone formation as shown by the reduced P1NP serum level as well as the reduced osteoid surfaces and bone formation rate in the femur. PTH injection in LP-SOY mice had no effect on total weight or lean mass, but improved all bone parameters at both femoral and vertebral sites, suggesting that amino acid deficiency was not the primary reason for degraded bone status in mice consuming soy protein. In conclusion, our study showed that under the same protein restriction (6% of energy), a soy diet leads to impaired bone health whereas a casein diet has little effect when compared to a normal protein control.

Dietary Protein and Bone Health

Dietary proteins represent 10 to 20% of energy consumption. The recommended daily minimum intake of protein and amino acids in adults is 0.8 g per kg of body weight. However, no upper limit has been identified. In industrialized countries, the main sources of protein are milk, eggs and meat. The nutritional value of protein is influenced by several factors, especially the amino acid (AA) composition, protein digestibility, protein digestion kinetics and the ability to transfer AA for protein synthesis. Diets based on either animal or vegetable products supply proteins of differing quality in differing quantities. Plant proteins are often deficient or low in some specific indispensable AAs. Soy protein is reported as a “complete” protein but its overall indispensable AA content is relatively low (~85% lower than milk) (Wilson & Wilson, 2006).