Animal models for the study of nutrition and human disease: colon cancer, atherosclerosis, and osteoporosis

Inflammatory serum proteome pattern in mice fed a high-fat diet

To investigate the influence of diet on serum protein pattern, mice were fed for 8 weeks either control chow or a high-fat diet (containing 21 % w/w milk fat and 0.2 % w/w cholesterol); sera were collected and analyzed by 2-DE. The main positive acute-phase reactant proteins, haptoglobin and hemopexin, were significantly up-regulated in animals receiving the high-fat diet. Data on all other proteins also pointed to an inflammatory condition in these animals. The largest change in concentration was observed for carboxylesterase N, a circulating enzyme seldom connected with lipid metabolism in earlier reports. These observations agree with the notion of a link between diet-induced hyperlipidemia and the inflammatory component of its cardiovascular sequels in humans, but the effects in the experimental animals are massive and obviously affect most of the major serum proteins.

Evidence for the existence of a soybean resistant protein that captures bile acid and stimulates its fecal excretion

Feeding HMF, an insoluble "high-molecular-weight fraction" from an industrial enzymatic digest of a soy protein isolate, increased the fecal excretion of bile acid concomitant with increased fecal nitrogen. An amino acid analysis revealed that this increased fecal nitrogen could be explained by an increase in the insoluble protein fraction. This suggests the existence of an indigestible protein or peptide that can be called a "resistant protein" in the feces. The presumed resistant protein was rich in hydrophobic amino acids and bound bile acid by hydrophobic interaction. The residual fraction of HMF obtained after in vitro pepsin and pancreatin digestion, showed higher in vitro bile acid-binding capacity and excreted more bile acid in vivo than HMF. Its amino acid composition was similar to that of the feces of rat fed with HMF. These results suggest that the fecal resistant protein with bile acid-binding ability could be derived from the indigestible fraction of HMF.

Identification of the bile acid-binding region in the soy glycinin A1aB1b subunit

Soy glycinin has five major subunits which are classified into two groups according to their homology in amino acid sequences (group I, A1aB1b, A1bB2 and A2B1a; group II, A3B4 and A5A4B3). It has been reported that the peptide fragments derived from the A1a and A2 chains of the A1aB1b and A2B1a subunits had bile acid-binding ability and that the region of 114-161 residues of the A1a chain was responsible for this bile acid-binding ability. In this study, we constructed A1a, A3 and 9 deletion mutants of A1a lacking various numbers of residues at the C-terminus, and evaluated their bile acid-binding ability by a cholic acid-conjugated column and fluorescence analysis. The bile acid-binding ability of A1a was higher than that of A3 and there was a remarkable decrease in the bile acid-binding ability between the delta[138-291] and delta[130-291] mutants. The 130-138 region is rich in hydrophobic residues. In this regard, when we constructed the delta[129-134] mutant lacking six contiguous hydrophobic residues (VAWWMY) and evaluated its bile acid-binding ability, a similar remarkable decrease in the bile acid-binding ability was observed. These results indicate that the 129-134 residue region (VAWWMY) with high hydrophobicity was important for bile acid-binding of A1a.

Soybean resistant proteins interrupt an enterohepatic circulation of bile acids and suppress liver tumorigenesis induced by azoxymethane and dietary deoxycholate in rats

We found that azoxymethane and dietary deoxycholate induced liver tumors in rats. The incidence and the development of the tumor were closely related to the enterohepatic circulation of bile acids. The feeding of a high-molecular-weight fraction of soy protein digest (HMF) suppressed the tumorigenesis, probably due to the inhibitory effect of soybean resistant protein on reabsorption of bile acids in the intestine.

A new method to isolate large numbers of rabbit osteoclasts and osteoclast-like cells: application to the characterization of serum response element binding proteins during osteoclast differentiation

We have developed a new method that allows the purification of large numbers of both authentic osteoclasts (OCs) and in vitro differentiated osteoclast-like cells (OCLs) from rabbits. We characterized the OCLs in terms of the expression of different phenotypic markers of OC differentiation and their ability to resorb bone. The method provides a system for performing biochemical and molecular studies of OC differentiation and function in a single species. We used this system to characterize the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the expression of proteins that bind to the serum response element (SRE) of the c-fos promoter. We found that OCLs and OCs displayed similar SRE-binding activities, including the serum response factor (SRF). This pattern is established in a time-dependent and cell-specific manner in response to long-term treatment of rabbit bone marrow by 1,25(OH)2D3. Thus, 1,25(OH)2D3 can modulate SRF and/or SRF-related protein. This finding may contribute to understanding the role of c-Fos in the regulation of OC differentiation.

Monoclonal antibody recognizing a determinant on type 2 chain blood group A and B oligosaccharides detects oncodevelopmental changes in azoxymethane-induced rat colon tumors and human colon cancer cell lines

Altered expression of ABH blood group substances is a common feature of human colorectal carcinoma, yet it remains unclear how these structural changes influence the biological properties of tumor cells. Azoxymethane-induced rat colon tumors display many features of the human disease, thereby providing a potentially useful model to study the role of blood group substances in colon cancer progression. We have prepared monoclonal antibodies to a microsomal fraction isolated from an azoxymethane-induced rat colon tumor and selected an antibody that detects cancer-associated changes. Monoclonal antibody (mAb) 3A7 recognizes a determinant on type 2 chain blood group A (GalNAc alpha 1-3[Fuc alpha 1-2]Gal beta 1-4GlcNAc-R) and B (Gal alpha 1-3[Fuc alpha 1-2]Gal beta 1-4GlcNAc-R) oligosaccharides. Expression of the epitope detected by this antibody was developmentally regulated in rat colon, with maximal expression from day 4-21 after birth. Immunohistochemical staining and Western blotting analyses of azoxymethane-induced colon tumors revealed increased expression of the epitope in all of the 21 colonic tumors examined, including preneoplastic glands within transitional mucosa. Conventional and signet-ring adenocarcinomas that had invaded through the muscularis propria (Duke's B2) consistently showed the most intense staining with mAb 3A7, including regions depicting angioinvasion. Some of the lymph node metastases (Duke's C2) stained poorly with the antibody. The epitope was also expressed in blood group A positive human colon carcinoma cell lines, including HT29 and SW480 but not by SW620, a cell line derived from a lymph node metastasis isolated in vivo from the SW480 primary tumor, or in the blood group B cell line SW1417. The glycoproteins detected by mAb 3A7 in rat colon tumors and HT29 cells ranged in size between 50 and 200 kd, including a major species of 140 kd. Affinity chromatography of detergent lysates of normal rat colon on the blood group A specific lectin Dolichos biflorus (DBA)-agarose resulted in nearly quantitative binding of glycoprotein species detected by the antibody. By contrast, immunoreactive glycoproteins from rat colon tumors or HT29 cells bound poorly to DBA-agarose but were retained by another blood group A-binding lectin, Helix-pomatia (HPA)-agarose. These results indicate that colon carcinogenesis results in quantitative as well as qualitative changes in oligosaccharides detected by mAb 3A7 and suggest that the combined use of mAb 3A7 and blood group A-specific lectins may provide a useful tool for early detection of colon cancer.

The effects of a "low-risk" diet on tumor incidence in chemically induced colon cancer in rats

The relationship between various dietary constituents and colon cancer has been demonstrated by previous research. We conducted a study to investigate the combined effects of several dietary constituents on intestinal tumor incidence in azoxymethane (AOM)-induced colon cancer in rats. A nutritionally adequate, "low-risk" (LR) diet was formulated through nonextreme dietary manipulations of dietary fat, fiber, protein, vitamins A and E, and selenium. Seventy-two female F344 weanling rats were given three weekly subcutaneous injections of either AOM or physiological saline solution, and were maintained on either the LR or a "high-risk" (HR) diet. Food consumption and body weights were monitored on a weekly basis throughout the study. Tumor incidence was determined 36 weeks following the first injection of AOM. The incidence of adenocarcinomas in the LR diet group was 4.2% compared with 29.2% in the HR diet group. There were no significant differences in the incidence of small intestinal tumors or in the incidence of benign polyps between the diet groups. The results of the study indicated a significant protective effect of the various chemopreventive dietary factors when combined in an LR diet for colon cancer.

The effects of a "low-risk" diet on cell proliferation and enzymatic parameters of preneoplastic rat colon

The relationship between various dietary constituents and colon cancer has been demonstrated by previous research. This study was conducted to investigate the combined effects of several dietary constituents on the preneoplastic stage of azoxymethane (AOM)-induced colon cancer in rats. A nutritionally adequate, "low-risk" (LR) diet was formulated through the modulation of dietary fat, fiber, protein, vitamins A and E, and selenium. Female F344 rats were given three weekly subcutaneous injections of AOM and were maintained on either the LR diet or a "high-risk" (HR) diet. After 12 weeks, the rats were killed and the following parameters were determined: pH of colon contents, fecal beta-glucuronidase activity, tissue ornithine decarboxylase (ODC) activity, and colonic labeling index. The pH of the colon contents and incremental labeling index were lower in the group given the LR diet and treated with AOM compared with the group given the HR diet and treated with AOM; however, no statistically significant dietary effects were observed for beta-glucuronidase and ODC activities. The results of this study indicated that the colons of rats fed the LR diet exhibited different proliferative characteristics than did the colons of rats fed the HR diet.