Diet, apoptosis, and carcinogenesis

Herbs or Natural Products That Protect Against Cancer Growth: Part Three of a Four-Part Series

PURPOSE/OBJECTIVES

To provide evidence-based research information about 47 herbs and natural products that have the potential to protect against the development of cancer.

DATA SOURCES

Natural Medicines Comprehensive Database and Lawrence Review of Natural Products-Monograph System. Information about these herbs has been found in evidence-based studies cited in the references.

DATA SYNTHESIS

Early research shows that some herbs and natural products appear to have the potential to prevent cancer growth.

CONCLUSIONS

This preliminary evidence may be useful to healthcare professionals or patients who are concerned about cancer.

IMPLICATIONS FOR NURSING

Oncology nurses who receive this information can become resources for patients or other healthcare professionals.

Modulation of apoptosis as a target for liver disease

Apoptosis mediated via extrinsic or intrinsic pathways is essential for maintaining cellular homeostasis in the liver. The extrinsic pathway is triggered from the cell surface by engagement of death receptors as CD95, TRAIL (TNF-related apoptosis inducing ligand) and TNF (tumour necrosis factor) or TGF-beta (transforming growth factor beta) receptors. The intrinsic pathway is initiated from the mitochondria and can be influenced by Bcl-2 family members. Both pathways are intertwined and play a physiological role in the liver. Dysregulation of apoptosis pathways contributes to diseases as hepatocellular carcinoma, viral hepatitis, autoimmune hepatitis, ischaemia-reperfusion injury, iron or copper deposition disorders, toxic liver damage and acute liver failure. The apoptosis defects are often central pathogenetic events; hence molecular mechanisms of apoptosis give not only insight into disease mechanisms but also provide potential corresponding therapeutic candidates in liver disease. The focus of this review is the identification of apoptotic signalling components in the liver as therapeutic targets.

Chronic low intake of protein or vitamins increases the intestinal epithelial cell apoptosis in Wistar/NIN rats

OBJECTIVE

Malnutrition decreases antioxidant defense and increases oxidative stress in the intestine. We studied the effects of long-term restriction of food, protein, and vitamins on intestinal epithelial cell (IEC) apoptosis and the underlying mechanisms.

METHODS

Weanling, Wistar/NIN male rats were fed ad libitum with a control diet, 75% protein-restricted diet, or 50% vitamin-restricted diet for 20 wk. The food-restricted group received 50% of the diet consumed by control rats. IEC apoptosis was monitored by morphometry, Annexin V binding, M30 CytoDeath assay, and DNA fragmentation. Structural and functional integrity of the villus were assessed by the ratio of villus height to crypt depth, and alkaline phosphatase and lys, ala-dipeptidyl aminopeptidase activities, respectively. Oxidative stress parameters, caspase-3 activity, and expression of Bcl-2 and Bax were determined to assess the probable mechanisms of altered apoptosis.

RESULTS

Protein and vitamin restrictions but not food restriction significantly increased IEC apoptosis and only vitamin restriction altered structural and functional integrity of villi. Increased levels of protein carbonyls, thiobarbituric acid reactive substances, and caspase-3 activity along with decreased glutathione levels and Bcl-2 expression were observed in IECs of these rats, whereas food restriction did not affect these parameters.

CONCLUSIONS

Protein restriction increased only IEC apoptosis, whereas vitamin restriction also affected the structure and function of villi. Modulation of the pathway mediated by mitochondria through increased oxidative stress appears to be the probable mechanism underlying this effect.

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.

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.

Increased uracil misincorporation in lymphocytes from folate-deficient rats

The development of certain human cancers has been linked with inadequate intake of folates. The effects of folate deficiency in vivo on DNA stability (strand breakage, misincorporated uracil and oxidative base damage) in lymphocytes isolated from rats fed a diet deficient in folic acid was determined. Because the metabolic pathways of folate and other methyl donors are closely coupled, the effects of methionine and choline deficiency alone or in combination with folate deficiency were determined. Feeding male Hooded Lister rats a folate-free diet for 10 weeks created a moderate folate deficiency (25-50% (approx.) decrease in plasma, red blood cell and hepatic folate concentrations (P < 0.05) and a 20% rise in plasma homocysteine (P < 0.05)). Lymphocyte DNA strand breakage was increased successively in all groups after 4 weeks and 8 weeks on the diet (50-100% (approx.) after 8 weeks). Only low folate specifically and progressively induced uracil misincorporation throughout the study (100% (approx.) after 8 weeks). Neither folate deficiency nor choline/methionine deficiency altered oxidative DNA base damage. In summary, moderate folate deficiency in vivo is associated with a decrease in DNA stability, measured as increased DNA strand breakage and misincorporated uracil.

Enhancement of hepatocarcinogenesis initiated with diethylnitrosamine or N-nitrosobis(2-hydroxypropyl)amine by a choline-deficient, L-amino acid-defined diet administered prior to the carcinogen exposure in rats

Effects of pre-administration of a choline-deficient, L-amino acid-defined (CDAA) diet on hepatocarcinogenesis initiated with diethylnitrosamine (DEN) or N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats were investigated. A pre-administrating period was set as 1 week, because CDAA diet induces liver injuries by this time-point. In a time-course study, male Fischer 344 rats, 6 weeks old, received a 1-week pre-administration of choline-supplemented, L-amino acid-defined (CSAA) or CDAA diet, DEN at a dose of 100 mg/kg body weight by a single intraperitoneal injection, then CSAA or CDAA diet for up to 8 weeks, and were sacrificed 4, 6 and 8 weeks after DEN. CDAA diet administered only after DEN significantly increased the numbers of glutathione S-transferase placental form (GST-P)-positive lesions 4, 6 and 8 weeks after DEN and their sizes 6 and 8 weeks after DEN. CDAA diet administered both before and after DEN similarly increased the numbers and sizes of GST-P-positive lesions, but with a significantly greater degree than obtained by the diet administered only after DEN. In a dose response study, rats received vechicle or DEN, at a dose of 0.001, 0.01, 0.1, 1, 10, 20, 50, 100 or 200 mg/kg body weight, 1 week after the commencement of CSAA or CDAA diet, and sacrificed 8 weeks after vehicle or DEN. The significant increases of the numbers of GST-P-positive lesions were obtained after 50-200 mg/kg body weight of DEN under the CSAA diet administration, whereas those were detected after 10-200 mg/kg under CDAA diet administration. Sizes became significantly larger with only 200 mg/kg body weight of DEN in the CSAA case but with 50-200 mg/kg in the CDAA case. Male Wistar rats received a 1-week pre-administration of CSAA or CDAA diet, vehicle or BHP, at a dose of 600 or 1200 mg/kg body weight, by a single intraperitoneal injection, then CSAA or CDAA diet for 8 weeks, and were then sacrificed. The numbers of GST-P-positive lesions demonstrated significant increment with 1200 mg/kg body weight of BHP by CDAA diet administered only after BHP and, to a significantly greater degree, by the diet administered both before and after BHP. While CDAA diet administered only after BHP did not alter the sizes of GST-P-positive lesions, the diet administered both before and after 600 and 1200 mg/kg body weight of BHP significantly increased the sizes of the lesions. These results indicate that the pre- plus post-administration of CDAA diet enhances hepatocarcinogenesis initiated with DEN or BHP, more than the post-administration only, thus providing a sensitive model to detect weak liver carcinogenic potency of environmental chemicals.

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.