Human apoA-I/C-III/A-IV gene cluster transgenic rabbits: effects of a high-cholesterol diet

Genetically modified rabbit models for cardiovascular medicine

Genetically modified (GM) rabbits are outstanding animal models for studying human genetic and acquired diseases. As such, GM rabbits that express human genes have been extensively used as models of cardiovascular disease. Rabbits are genetically modified via prokaryotic microinjection. Through this process, genes are randomly integrated into the rabbit genome. Moreover, gene targeting in embryonic stem (ES) cells is a powerful tool for understanding gene function. However, rabbits lack stable ES cell lines. Therefore, ES-dependent gene targeting is not possible in rabbits. Nevertheless, the RNA interference technique is rapidly becoming a useful experimental tool that enables researchers to knock down specific gene expression, which leads to the genetic modification of rabbits. Recently, with the emergence of new genetic technology, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated protein 9 (CRISPR/Cas9), major breakthroughs have been made in rabbit gene targeting. Using these novel genetic techniques, researchers have successfully modified knockout (KO) rabbit models. In this paper, we aimed to review the recent advances in GM technology in rabbits and highlight their application as models for cardiovascular medicine.

Genetically Modified Rabbits for Cardiovascular Research

Rabbits are one of the most used experimental animals for investigating the mechanisms of human cardiovascular disease and lipid metabolism because they are phylogenetically closer to human than rodents (mice and rats). Cholesterol-fed wild-type rabbits were first used to study human atherosclerosis more than 100 years ago and are still playing an important role in cardiovascular research. Furthermore, transgenic rabbits generated by pronuclear microinjection provided another means to investigate many gene functions associated with human disease. Because of the lack of both rabbit embryonic stem cells and the genome information, for a long time, it has been a dream for scientists to obtain knockout rabbits generated by homologous recombination-based genomic manipulation as in mice. This obstacle has greatly hampered using genetically modified rabbits to disclose the molecular mechanisms of many human diseases. The advent of genome editing technologies has dramatically extended the applications of experimental animals including rabbits. In this review, we will update genetically modified rabbits, including transgenic, knock-out, and knock-in rabbits during the past decades regarding their use in cardiovascular research and point out the perspectives in future.

Transgenic Rabbit Models: Now and the Future

Transgenic rabbits have contributed to the progress of biomedical science as human disease models because of their unique features, such as the lipid metabolism system similar to humans and medium body size that facilitates handling and experimental manipulation. In fact, many useful transgenic rabbits have been generated and used in research fields such as lipid metabolism and atherosclerosis, cardiac failure, immunology, and oncogenesis. However, there have been long-term problems, namely that the transgenic efficiency when using pronuclear microinjection is low compared with transgenic mice and production of knockout rabbits is impossible owing to the lack of embryonic stem cells for gene targeting in rabbits. Despite these limitations, the emergence of novel genome editing technology has changed the production of genetically modified animals including the rabbit. We are finally able to produce both transgenic and knockout rabbit models to analyze gain- and loss-of-functions of specific genes. It is expected that the use of genetically modified rabbits will extend to various research fields. In this review, we describe the unique features of rabbits as laboratory animals, the current status of their development and use, and future perspectives of transgenic rabbit models for human diseases.

Water extracts of cinnamon and clove exhibits potent inhibition of protein glycation and anti-atherosclerotic activity in vitro and in vivo hypolipidemic activity in zebrafish

Advanced glycation end products contribute to the pathogenesis of diabetic complications and atherosclerosis. Aqueous extracts of ground pepper, cinnamon, rosemary, ginger, and clove were analyzed and tested for anti-atherosclerotic activity in vitro and in vivo using hypercholesterolemic zebrafish. Cinnamon and clove extracts (at final 10 μg/mL) had the strongest anti-glycation and antioxidant activity in this study. Cinnamon and clove had the strongest inhibition of activity against copper-mediated low-density lipoprotein (LDL) oxidation and LDL phagocytosis by macrophages. Cinnamon or clove extracts had potent cholesteryl ester transfer protein (CETP) inhibitory activity in a concentration-dependent manner. They exhibited hypolipidemic activity in a hypercholesterolemic zebrafish model; the clove extract-treated group had a 68% and 80% decrease in serum cholesterol and TG levels, respectively. The clove extract-fed group had the smallest increase in body weight and height and the strongest antioxidant activity following a 5-week high cholesterol diet. Hydrophilic ingredients of cinnamon and clove showed potent activities to suppress the incidence of atherosclerosis and diabetes via strong antioxidant potential, prevention of apoA-I glycation and LDL-phagocytosis, inhibition of CETP, and hypolipidemic activity. These results suggest the potential to develop a new functional dietary agent to treat chronic metabolic diseases, such as hyperlipidemia and diabetes.

Glutamine regulates the expression of proteins with a potential health-promoting effect in human intestinal Caco-2 cells

Glutamine is an essential amino acid for the enterocytes with respect to maintaining the gut mucosal integrity and function. This study was conducted to explore a molecular basis for the beneficial effects of glutamine on intestinal cells by searching for glutamine-dependent changes in the proteome. Caco-2 cells were exposed to different concentrations of L-glutamine with or without L-methionine sulfoximine, an inhibitor of the glutamine synthetase activity. 2-DE combined with MALDI-TOF-MS was used to identify proteins whose expression is changed by glutamine. To assess the relative protein synthesis rate, incorporation of L-[2H5]glutamine into individual proteins was monitored. The expression levels of 14 proteins changed significantly with the glutamine availability. Examples of differentially expressed proteins with potential health-promoting effects on the intestine are plasma retinol-binding protein, ornithine aminotransferase, apolipoprotein A-I, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, and acyl-CoA synthetase 5. Expression of these proteins was not changed by arginine deprivation. The differential change in the expression levels of the proteins was not correlated with their rate of synthesis, excluding an effect of glutamine depletion on general protein synthesis. Together, this study shows a gene-specific effect of glutamine on intestinal cells.