Early and late effects of wound healing on development of colon tumours in a model of colon carcinogenesis by 1,2-dimethylhydrazine in the rat

Vitamin E supplementation in chemical colorectal carcinogenesis: a two-edged knife

This work investigated the effects of Vitamin E (VE) on aberrant crypt foci (ACF) incidence, oxidative stress parameters (serum and hepatic VE concentration, and homocysteine, glutathione (GSH), and malondialdehyde (MDA) levels), and expression of both cyclooxygenase-2 (COX2) and proliferating cellular nuclear antigen (PCNA) in experimental colorectal carcinogenesis. Male Wistar rats received subcutaneous injections of 1,2-dimethylhydrazine (DMH) twice a week, for two weeks (40 mg/kg), except for the Control group. Animals were separated into groups that received different amounts of VE in the diet: 0 IU (0×), 75 IU (recommended daily intake, RDI), 225 IU (3× RDI), or 1500 IU (20× RDI), during (dDMH) or after (aDMH) administration of carcinogen. The 0×dDMH and 3×dDMH groups showed decreased serum VE levels. Hepatic VE concentration was higher in 3×aDMH as compared with the other groups. All the groups, except the Control and the 0×aDMH groups, had reduced GSH levels. The 0×dDMH, 0×aDMH, and 20×aDMH groups exhibited increased MDA levels. The aDMH groups had higher ACF incidence and PCNA expression. The 0×aDMH group presented higher ACF rate, followed by 20×aDMH. Moreover, the 3×aDMH group displayed reduced ACF incidence and COX2 expression. Multivariate analysis revealed that GSH modulated homocysteine levels and COX2. These results suggested that 1500 IU of VE is hazardous, whereas 225 IU of VE has beneficial effects on chemical colorectal carcinogenesis.

Zinc and zinc related enzymes in precancerous and cancerous tissue in the colon of dimethyl hydrazine treated rats

Trace element zinc deficiency or excess is implicated in the development or progression of some cancers. The exact role of zinc in the etiology of colon cancer is unclear. To cast light on this question, an experimental model of colon carcinogenesis was applied here. Six week old rats were given sub cutaneous injections of DMH (30 mg/kg body weight) twice a week for three months and sacrificed after 4 months (precancer model) and 6 months (cancer model). Plasma zinc levels showed a significant decrease (p<0.05) at 4 months and a greater significant decrease at 6 months (p<0.01) as compared with controls. In the large intestine there was a significant decrease in tissue zinc levels (p<0.005) and in CuZnSOD, and alkaline phosphatase activity (p<0.05) in the pre-cancerous model and a greater significant decrease in tissue zinc (p<0.0001), and in CuZnSOD and alkaline phosphatase activity (p<0.001), in the carcinoma model. The tissue zinc levels showed a significant decrease in the small intestine and stomach (p<0.005) and in liver (p<0.05) in the cancer model. 87% of the rats in the precancer group and 92% rats in the cancer group showed histological evidence of precancerous lesions and carcinomas respectively in the colon mucosa. This study suggests that the decrease in plasma zinc, tissue zinc and activity of zinc related enzymes are associated with the development of preneoplastic lesions and these biochemical parameters further decrease with progression to carcinoma in the colon.

Surgery and cancer promotion: are we trading beauty for cancer?

It is well-known that cancer surgery can actually promote the growth of some tumors by a variety of mechanisms. There are observational data suggesting that surgery per se can increase the risk of cancer among individuals without a history of clinical cancer. Occult microscopic cancers are exceedingly common in the general population and are held in a dormant state by a balance between cell proliferation and cell death and also an intact host immune surveillance. The catecholamine surge from the stress of surgery and resulting β(2)-adrenergic signaling culminates in a transient and robust increased vascular endothelial growth factor expression locally and systemically that is enough to start tumor angiogenesis and end dormancy. The same catecholamine surge and β(2)-adrenergic signaling impairs cell-mediated immunity at a crucial time. Elegant animal studies have demonstrated that perioperative nonselective β-blockade abrogates surgical stress-induced angiogenesis and tumor growth. Prospective human trials are desperately needed and clinical implications are discussed.

Rat models of skin wound healing: a review

Rats have been widely used in the study of skin wound healing and the efficacy of different treatment modalities. This particular animal species is often selected for its availability, low cost, and small size. To define the current use of rat skin wound healing models, this manuscript provides a review of articles published between 2000 and 2003 that chose rats as their research animals. Of the 55 articles reviewed, it was found that 38.2% of the studies used incisional models and 38.2% used excisional models, with some studies using combinations. The majority of the studies (78.2%) used the rat's dorsum as the wound location. Male Sprague Dawley in the 250-300 gram weight range were the most preferred rats. Sodium pentobarbital/pentobarbitone was the most commonly used anesthetic choice. Similarities and differences in the selected experimental conditions are noted and questions are raised with regard to comparability between studies and the ability to transfer the data from the animal model to the human clinical situation. Attempts to compare studies for the advancement of wound healing knowledge are being hampered by the differences found between the studies. Standardization in reporting could facilitate comparisons and may instigate additional research that favors the inevitable comparisons between the studies. Thus, universal reporting requirements need to be developed for animal wound healing studies.

Aberrant crypt foci and colon cancer: comparison between a short- and medium-term bioassay for colon carcinogenesis using dimethylhydrazine in Wistar rats

Aberrant crypt foci (ACF) in the colon of carcinogen-treated rodents are considered to be the earliest hallmark of colon carcinogenesis. In the present study the relationship between a short-term (4 weeks) and medium-term (30 weeks) assay was assessed in a model of colon carcinogenesis induced by dimethylhydrazine (DMH) in the rat. Six-week-old male Wistar rats were given subcutaneous injections of DMH (40 mg/kg) twice a week for 2 weeks and killed at the end of the 4th or 30th week. ACF were scored for number, distribution pattern along the colon and crypt multiplicity in 0.1% methylene-blue whole-mount preparations. ACF were distinguished from normal crypts by their larger size and elliptical shape. The incidence, distribution and morphology of colon tumors were recorded. The majority of ACF were present in the middle and distal colon of DMH-treated rats and their number increased with time. By the 4th week, 91.5% ACF were composed of one or two crypts and 8.5% had three or more crypts, while by the 30th week 46.9% ACF had three or more crypts. Thus, a progression of ACF consisting of multiple crypts was observed from the 4th to the 30th week. Nine well-differentiated adenocarcinomas were found in 10 rats by the 30th week. Seven tumors were located in the distal colon and two in the middle colon. No tumor was found in the proximal colon. The present data indicate that induction of ACF by DMH in the short-term (4 weeks) assay was correlated with development of well-differentiated adenocarcinomas in the medium-term (30 weeks) assay.