Choline deficiency induces apoptosis and decreases the number of eosinophilic preneoplastic foci in the liver of OXYS rats

Hypothesis: Chronic Progressive Nephropathy in Rodents as a Disease Caused by an Expanding Somatic Mutant Clone

Chronic progressive nephropathy is a common noninfectious disease in aging (mice, rats) and non-aging (naked mole rat) rodents, sometimes resulting in death. The etiology and pathogenesis of the disease remain mysterious. For instance, it remains unclear what is the immediate cause of the disease and where exactly in the kidneys, glomerular or tubulointerstitial compartment, do primary and secondary changes occur. Here, I propose a potential scenario for development of progressive nephropathy that is based on an assumption that the disease is caused by occurrence and spread of mutant cellular clones from tubular epithelium secreting proinflammatory and prosclerotic cytokines. The hypothesis considers some features of the disease that have never been discussed earlier. According to the proposed concept, a clone of mutant cells secretes cytokines inducing chronic inflammation, proliferation of fibroblasts, and active collagen production that eventually results in sclerosis and thickening of tubular basement membranes. Sclerosis of interstitium and thickening of tubular basement membranes cause narrowing of some parts of the nephron, especially collecting ducts, which hinders passage of the urine, elevates tubular hydrostatic pressure, and impairs filtration and reabsorption in the kidneys. High hydrostatic pressure and reabsorption-induced elevated concentration of macromolecular substances in the primary urine result in development of large cysts and glomerular hyalinosis followed by renal failure. Based on this, it might be concluded that chronic progressive nephropathy in rodents represents a special type of tubulointerstitial dysplasia (or "non-tumorous neoplasia") in kidneys with secondary glomerular disorder at late stage of the disease. The concept for development of the disease proposed here may be of special importance from the viewpoint of toxicological pathology and gerontology, particularly for analysis of pathological features resulting in death of non-aging animals (naked mole rats).

Animal models of age-related macular degeneration and their translatability into the clinic

Age-related macular degeneration (AMD) is a leading cause of blindness in people over the age of 55. Despite its common nature, the etiology of the disease involves both genetic and environmental factors, the interaction of which is not fully understood. Animal models, including the mouse, rat, rabbit, pig and non-human primate, have been developed to study various aspects of the disease and to evaluate novel therapies; however, no single model has been developed to emulate all aspects of the disease. This review will discuss the various existing models of AMD, their strengths and limitations and examples of their use in current AMD research.

Methionine- and choline-deficient diet induces hepatic changes characteristic of non-alcoholic steatohepatitis

CONTEXT: Non-alcoholic steatohepatitis is a disease with a high incidence, difficult diagnosis, and as yet no effective treatment. So, the use of experimental models for non-alcoholic steatohepatitis induction and the study of its routes of development have been studied. OBJECTIVES: This study was designed to develop an experimental model of non-alcoholic steatohepatitis based on a methionine- and choline-deficient diet that is manufactured in Brazil so as to evaluate the liver alterations resulting from the disorder. METHODS: Thirty male C57BL6 mice divided in two groups (n = 15) were used: the experimental group fed a methionine- and choline-deficient diet manufactured by Brazilian company PragSoluções®, and the control group fed a normal diet, for a period of 2 weeks. The animals were then killed by exsanguination to sample blood for systemic biochemical analyses, and subsequently submitted to laparotomy with total hepatectomy and preparation of the material for histological analysis. The statistical analysis was done using the Student's t-test for independent samples, with significance level of 5%. RESULTS: The mice that received the methionine- and choline-deficient diet showed weight loss and significant increase in hepatic damage enzymes, as well as decreased systemic levels of glycemia, triglycerides, total cholesterol, HDL and VLDL. The diagnosis of non-alcoholic steatohepatitis was performed in 100% of the mice that were fed the methionine- and choline-deficient diet. All non-alcoholic steatohepatitis animals showed some degree of macrovesicular steatosis, ballooning, and inflammatory process. None of the animals which were fed the control diet presented histological alterations. All non-alcoholic steatohepatitis animals showed significantly increased lipoperoxidation and antioxidant enzyme GSH activity. CONCLUSION: The low cost and easily accessible methionine- and choline-deficient diet explored in this study is highly effective in inducing steatosis and steatohepatitis in animal model, alterations that are similar to those observed in human livers.

The relation between d-galactose injection and mitochondrial DNA 4834bp deletion mutation

Since,D-galactose (D-gal) overload model has been used as a premature aging model, we hypothesized that it may also lead to accelerated aging in the inner ear. Furthermore, though the mitochondrial DNA (mtDNA) 4834 bp deletion mutation has been considered as the marker of aging, there is no information available in the literature concerning the mtDNA 4834 bp deletion mutation condition of the D-gal induced premature aging model. We investigate the changes in inner ear enzymatic activity, the occurring of mtDNA 4834 bp deletion in inner ear and other tissues and the relating hearing thresholds after the administration of high dosage (150 mg/kg per day) and low dosage (50 mg/kg per day) of D-gal to rats. Furthermore, the incidence of the mtDNA 4834 bp deletion in different tissues as well as in blood sample was compared. The results showed that daily subcutaneous injections of D-gal into rats for 8 weeks could lead to the biochemical defects and mtDNA 4834 bp deletion in the inner ear tissue and other tissues, which represent the typical aging animals, but the relating hearing threshold shifts (TS) were nearly identical in the three groups. This study also indicates that using of blood samples to detect mtDNA 4834 bp deletion in clinical research might lead to a 'false negative' result. A higher sensitive result could be gained using tissue biopsy to examine mtDNA 4834 bp deletion.

Cataract formation in a strain of rats selected for high oxidative stress

The primary purpose of this study was to define the clinical and morphological features of cataractogenesis in the OXYS strain of rats that generate excess reactive oxygen species. Rats were sequentially examined from birth to the development of mature cataracts with slit lamp biomicroscopy. Morphology of selected stages of cataract development was studied using light and transmission electron microscopy (TEM), immunohistochemical localization of the lipid peroxidation product 4-hydroxynonenal (HNE) and fluorescent antibody labeling for DNA oxidation products. Lenses from age-matched normal rats were used as controls. OXYS rats developed cataracts as young as two weeks of age with progression to maturity by 1 year. Clinically, cataracts appeared initially either as nuclear or sub-capsular cortical changes and progressed to pronounced nuclear cataracts within months. TEM confirmed the light microscopic impression of region-specific alterations in both fiber cell cytoplasmic protein matrix and membrane structure. The outer adult nuclear region showed extensive cellular damage similar to osmotic cataracts, which is consistent with the postulated high uptake of glucose in the OXYS strain. The adult and outer fetal nuclear cells displayed several types of focal damage. The inner fetal and embryonic nuclear cells demonstrated textured cytoplasm, suggesting protein degradation or redistribution. Staining for HNE was increased in epithelium, cortex and nucleus compared to control lenses. Fluorescent antibody probes demonstrated increased levels of DNA oxidation products in OXYS rat lenses compared to age-matched controls. Fourier analysis of nuclear cytoplasm revealed significant components with corresponding sizes greater than 100 nm and, using a new theoretical approach, the texturing of the cytoplasm was shown to be sufficient to cause opacification of the nucleus. The OXYS rat appears to be an ideal model for oxidative stress cataractogenesis. The potential oxidative damage observed is extensive and characteristic of the developmental region. The source of oxidative damage may in part be a response to elevated levels of glucose. Because oxidative stress is thought to be a major factor in cataract formation in both diabetic and non-diabetic aging humans, this animal model may be a useful tool in assessing efficacy of antioxidant treatments that may slow or prevent cataract formation.

Investigations on cell proliferation in B6C3F(1) mouse liver by diethanolamine

Diethanolamine (DEA) has been shown to induce liver tumours in B6C3F(1) mice in a previous 2-year dermal study. To elucidate the mode of action groups of eight male and eight female B6C3F1 mice were dermally exposed to daily DEA doses of 0 or 160 mg/kg body weight/day for 1 week. Reversibility was assessed after a 3-week treatment-free recovery period. Subsequently groups of 10 male B6C3F(1) mice were dermally exposed to daily DEA doses of 0 or 160 mg/kg body weight for 1, 4 or 13 weeks. Finally, groups of 8 male B6C3F(1) mice were dermally exposed to daily DEA doses of 0, 10, 20, 40, 80, and 160 mg/kg body weight for 1 and 13 weeks. Following a 1-week treatment, DEA caused increased cell proliferation (5-bromo-2'-deoxyuridine (BrdU) method) in zone 3 (central vein region) of the liver lobules at 160 mg/kg body weight. Reversibility of liver cell proliferation was demonstrated in the recovery phase. In the subsequent studies increased cell proliferation was observed at 10 mg/kg body weight or higher after 13 weeks of treatment. These results support the hypothesis that sustained liver cell proliferation is a potential non genotoxic mode of action by which DEA promotes liver tumours in B6C3F(1) mice.

Prenatal choline deficiency decreases the cross-sectional area of cholinergic neurons in the medial septal nucleus

Levels of dietary choline in utero influence postnatal cognitive performance. To better understand this phenomenon, forebrain cholinergic neurons were studied in the 8-9 month old offspring of dams fed a control or choline-deficient diet from EDs 11-17. Serial sections were immunostained with antibodies against p75, a cholinergic marker. Neuronal morphology was analyzed in the basal forebrain, a heterogeneous area composed of several structures including the medial septal nucleus (MSN), nucleus of the diagonal band (DB), and the nucleus basalis of Meynert (NB). Neuronal cross-sectional areas were selectively reduced in the MSN of choline-deficient animals, compared to controls, but cell counts were not altered. Our findings suggest that cholinergic medial septal neurons may be selectively vulnerable to in utero choline deficiency.

Activation of a caspase-dependent oxidative damage response mediates TGFbeta1 apoptosis in rat hepatocytes

Activation of transforming growth factor-beta type 1- (TGFbeta1) mediated signaling occurs in response to cell injury affecting stem-type cells and hepatocytes in liver. In this work we used WB stemlike liver epithelial cells and p53-defective CWSV-1 nontumorigenic rat hepatocytes to investigate the possible roles of caspases and oxidative stress in TGFbeta1 signaling. TGFbeta1 significantly increased the level of 4-hydroxy-2-nonenal (4-HNE), a stable product of lipid peroxidation. In addition, TGFbeta1-treated cells exhibited activation of caspases that accompanied by enhanced cleavage of the caspase substrate poly(ADP)-ribose polymerase (PARP) and induction of apoptosis. WB cells were twice as sensitive as sensitive as CWSV-1 cells to induction of TGFbeta1 apoptosis. TGFbeta1-apoptosis was significantly reduced when cells were treated with TGFbeta1 in the presence of inhibitors of caspase-1, -3, -8, and -9. Importantly, in addition to suppression of apoptosis, treatment of cells with the caspase-3 inhibitor Z-DEVD-FMK in the presence of TGFbeta1 suppressed the formation 4-HNE and restored mitotic activity. Together, these data suggest TGFbeta1 induces activation of a caspase signaling cascade that includes an oxidative damage response, PARP cleavage, and apoptosis that do not require intact p53 in rat hepatocytes.

cAMP enhances Cx43 gap junction formation and function and reverses choline deficiency apoptosis

Previously, it had been shown that acute choline deficiency (CD) induced apoptosis in cultured rat liver epithelial cells, whereas cells that are adapted to survive in low-choline-containing medium acquire resistance to CD apoptosis and undergo malignant transformation. Thus, understanding the mechanisms of action of CD could increase our understanding of the role of choline, an essential nutrient, in the process of malignant transformation. The present experiments were designed to test the hypothesis that CD might function as a pro-apoptotic trigger by altering the localization of connexin 43 gap junction protein and gap junctional intercellular communication (GJIC). Established liver epithelial cells (WB cells; Hep3B cells) were maintained in a defined, serum-free medium control (70 microM choline) or choline deficient medium (CD, 5 microM choline) and the localization of connexin 43 protein (Cx43) was studied by immunocytochemistry and Western blotting. In nontumorigenic WB cells, CD apoptosis was associated with retention of Cx43 in the golgi/ER region of the cytoplasm and decreased GJIC as measured using a preloading fluorescent dye transfer method (calcein AM/DiIC(18)). Cells maintained in CD in the presence of 8-bromoadenosine 3':5'-cyclic monophosphate exhibited restoration of Cx43 at the plasma membrane and increased GJIC and inhibition of apoptosis. These studies show that CD apoptosis in nontumorigenic liver epithelial cells is associated with alterations to Cx43 and GJIC and that an uncoupling of Cx43 localization and GJIC is related to resistance to CD apoptosis in transformed liver epithelial cells.

Choline deficiency induced by Mycoplasma fermentans enhances apoptosis of rat astrocytes

A choline uptake system accumulating free choline in an energy-dependent process is described in Mycoplasma fermentans. The uptake system has a K(m) of 2.2x10(-5) M and a V(max) of 0.15 nmol 10 min(-1) mg(-1) cell protein and the choline incorporated could be recovered in the soluble fraction as free choline, phosphorylcholine and CDP-choline. Choline accumulation by M. fermentans resulted in a marked choline depletion of the growth medium. The choline depletion of an astrocyte cell culture induced by M. fermentans was associated with the apoptotic death of the cells. Apoptosis was not obtained with heat-inactivated mycoplasmas and could be reversed by the addition of free choline to the growth medium.

Regulation of mammalian cell membrane biosynthesis

This review explores current information on the interrelationship between phospholipid biochemistry and cell biology. Phosphatidylcholine is the most abundant phospholipid and it biosynthesis has been studied extensively. The choline cytidylyltransferase regulates phosphatidylcholine production, and recent advances in our understanding of the mechanisms that govern cytidylyltransferase include the discovery of multiple isoforms and a more complete understanding of the lipid regulation of enzyme activity. Similarities between phosphatidylcholine formation and the phosphatidylethanolamine and phosphatidylinositol biosynthetic pathways are discussed, together with current insight into control mechanisms. Membrane phospholipid doubling during cell cycle progression is a function of periodic biosynthesis and degradation. Membrane homeostasis is maintained by a phospholipase A-mediated degradation of excess phospholipid, whereas insufficient phosphatidylcholine triggers apoptosis in cells.

Endogenous liver carcinogenesis in the rat

Carcinogenesis may be effected not only through exposure to exogenous stimuli but also by genetic and epigenetic influences derived from endogenous factors. In the latter case, the mechanisms are still largely obscure because of the limited availability of appropriate in vivo experimental models. However, continuous feeding of a diet deficient in choline and methionine is well known to cause hepatocellular carcinomas (HCC) in rats in the absence of any known exogenous carcinogens and can serve as a good research model. A semi-synthetic, choline-deficient, L-amino acid-defined (CDAA) diet, containing practically no choline and low methionine, induces HCC with a background of fatty liver and hepatocyte death, subsequent regeneration and fibrosis resulting in cirrhosis. Using the CDAA diet, we have revealed the participation of oxidative injury to DNA and other subcellular components and of alteration in intrahepatic signal transduction pathways in the mechanisms underlying this rat liver carcinogenesis model. In the present paper, the current understanding of endogenous rat liver carcinogenesis, due to dietary choline deficiency, is reviewed.