Effect of bisacodyl and cascara on growth of aberrant crypt foci and malignant tumors in the rat colon.

Laxatives abuse has been associated with an increased risk for colon cancer. However, little is known about laxatives long-term carcinogenic potential in experimental studies. The present study was designed to investigate the effects of bisacodyl (4.3 and 43 mg/kg) and cascara (140 and 420 mg/kg) on azoxymethane (AOM)-induced aberrant crypt foci (ACF) and tumors. Animals, divided in 10 groups were treated with AOM and laxatives (alone or in combination) for 13 weeks. At the end of treatment animals were killed and the colon removed and analysed for the determination of ACF and tumors. Bisacodyl (4.3 and 43 mg/kg), given alone, did not induce the development of colonic ACF and tumors. Bisacodyl (4.3 mg/kg) coupled with AOM increased the number of crypt per focus, but not the number of tumors. Bisacodyl (43 mg/kg) significantly increased the number of crypt per focus and tumors. Cascara (140 and 420 mg/kg) did not induce the development of colonic ACF and tumors and did not modify the number of AOM-induced ACF and tumors. The results of the present study indicate a possible promoting effect of bisacodyl on rat colon carcinogenesis (especially at higher doses) and absence of any promoting or initiating activity of a laxative and diarrhoeal dose of cascara.     

Diallyl sulfide enhances azoxymethane-induced preneoplasia in Fischer 344 rat colon

Azoxymethane (AOM) is an indirect-acting colon carcinogen that produces a high incidence of precancerous lesions, referred to as aberrant crypt foci (ACF), in rats. This study was undertaken to determine whether high dose gavage administration of the cytochrome P-450 2E1 (CYP2E1) inhibitor and chemopreventive agent, diallyl sulfide, would reduce the incidence and severity of ACF formation in the distal colons of AOM-treated Fischer 344 rats. Seven-week-old male rats received 150 or 50 mg/kg diallyl sulfide by gavage 24 and 2 h prior to two weekly i.p. injections of AOM (20 mg/kg). Ten weeks after the last injection of AOM the rats were sacrificed and the colons removed and stained with 0.2% methylene blue. ACF were visualized using stereomicroscopy. Rats pretreated with diallyl sulfide exhibited a significant increase in the number of ACF/cm in the distal colon compared with rats receiving AOM alone. This increase in ACF number was seen in ACF of all sizes. To examine the effects of diallyl sulfide on the initiation stage of AOM-induced carcinogenesis, mutations in the K-ras proto-oncogene were also investigated. ACF and normal appearing colonic mucosa (0.2-0.5 mm3) were microdissected for subsequent PCR-RFLP analysis of a codon 12 (GGT-GGA) activating mutation in the K-ras gene. Greater than 90% of ACF from AOM-treated animals, regardless of diallyl sulfide treatment, exhibited activating K-ras mutations. K-ras mutations were also detected in normal appearing mucosa of AOM-treated animals, although at a lesser frequency (15-35%). These studies demonstrate that diallyl sulfide given in large gavage doses enhances AOM-induced preneoplasia in rats and suggests that diallyl sulfide may alter the disposition of AOM intermediates and/or enhance colonic promotional activity in the rat.     

Multivitamin and mineral supplementation in 1,2-dimethylhydrazine induced experimental colon carcinogenesis and evaluation of free radical status, antioxidant potential, and incidence of ACF

This study was performed to determine the chemopreventive and antioxidant status of multivitamin and mineral (0.01% in drinking water, ad libitum) supplements in 1,2-dimethylhydrazine (DMH)-induced experimental colon carcinogenesis. Experimental colon carcinogenesis was induced in male albino Wistar rats by injecting DMH (20 mg·(kg body mass)(-1)) once weekly for 15 consecutive weeks, and administering a multivitamin supplement in 3 regimes (initiation, post-initiation, and entire experimental period) for 32 weeks. We studied lipid peroxidation products (thiobarbituric acid reactive substances, lipid hydroperoxides, conjugated dienes) in the circulation and in the tissues, antioxidant status (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and non-enzymatic antioxidant-reduced glutathione) of the tissues, aberrant crypt foci (ACF), and histopathological alterations. DMH-induced rats had an increase in lipid peroxidation products and a lower antioxidant status compared with control animals. Multivitamin and mineral supplementation during the initiation, post-initiation, and the entire study period significantly decreased the levels of lipid peroxidation products in circulation and colonic tissues, significantly elevated the activities of the antioxidant enzymes and reduced glutathione to near normalcy in DMH-induced rats. The incidence of ACF was reduced by [corrected] 84.1% in rats supplemented with multivitamin and minerals for the entire study and prevented the colonic tissue from histopathological alterations induced by DMH.     

Chemoprevention of azoxymethane-induced rat aberrant crypt foci by dietary zerumbone isolated from Zingiber zerumbet.

The modifying effects of dietary feeding of zerumbone isolated from Zingiber zerumbet on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats. Expression of cyclooxygenase (COX)-2 in colonic mucosa exposed to AOM and/or zerumbone was also assayed. In addition, we assessed the effects of zerumbone on cell proliferation activity of crypts by counting silver-stained nucleolar organizer regions protein (AgNORs) in colonic cryptal cell nuclei. To induce ACF rats were given three weekly subcutaneous injections of AOM (15 mg/kg body weight). They were also fed the experimental diet containing 0.01% or 0.05% zerumbone for 5 weeks, starting one week before the first dosing of AOM. AOM exposure produced 84+/-13 ACF/rat at the end of the study (week 5). Dietary administration of zerumbone caused reduction in the frequency of ACF: 72+/-17 (14% reduction) at a dose of 0.01% and 45+/-18 (46% reduction, p<0.001) at a dose of 0.05%. Feeding of zerumbone significantly reduced expression of COX-2 and prostaglandins in colonic mucosa. Zerumbone feeding significantly lowered the number of AgNORs in colonic crypt cell nuclei. These findings might suggest possible chemopreventive ability of zerumbone, through suppression of COX-2 expression, cell proliferating activity of colonic mucosa, and induction of phase II detoxification enzymes in the development of carcinogen-induced ACF.     

Effects of high amylose maize starch and Clostridium butyricum on metabolism in colonic microbiota and formation of azoxymethane-induced aberrant crypt foci in the rat colon

High amylose maize starch (HAS) is not digested in the small intestine and most of it reaches the large intestine. In the large intestine, HAS is fermented by intestinal bacteria, resulting in production of short-chain fatty acids (SCFA), particularly butyrate. Clostridium butyricum can utilize HAS and produce butyrate and acetate. It has been proposed that butyrate inhibits carcinogenesis in the colon. In this study, we examined the inhibitory effects of HAS and C. butyricum strain MIYAIRI588 (CBM588) on azoxymethane-induced aberrant crypt foci (ACF) formation in rats. In the group of rats administered only CBM588 spores, the concentration of butyrate in the cecum increased, but there was no decrease in the number of ACF. In the group of rats fed an HAS diet, a decrease in the number of ACF was observed, and in the group of rats administered HAS and CBM588, the number of ACF decreased significantly. In these two groups, the concentrations of acetate and propionate in intestinal contents significantly increased, but the concentration of butyrate did not change. It was found that the beta-glucuronidase activity level of colonic contents decreased significantly in the two groups of rats fed HAS. This study showed that HAS and CBM588 changed the metabolism of colonic microbiota and decreased the level of beta-glucuronidase activity, phenomena that may play a role in the inhibition of ACF formation in the rat colon.     

Tumor-enhancing effects of cholic acid are exerted on the early stages of colon carcinogenesis via induction of aberrant crypt foci with an enhanced growth phenotype.

The objective of the study was to establish whether cholic acid (CHA) enhanced colonic tumor incidence in the early phase of carcinogenesis. Male, Sprague-Dawley rats (n = 180) were injected twice with azoxymethane (AOM) (15 mg x kg(-1) body weight x week(-1), s.c., given 1 week apart). Following the first AOM injection, animals were randomly assigned to two groups, control AIN-93G diet (CON) or control diet containing 0.2% CHA by weight (CHA). Three weeks after the first injection, 20 animals (10 animals/group) were killed and aberrant crypt foci (ACF) were enumerated. The remaining animals were further subdivided and animals randomly assigned to CON or CHA diets, creating four treatments: CON-CON, CON-CHA, CHA-CHA, and CHA-CON. After 3, 12, and 20 weeks (following the first carcinogen injection), the animals were killed and the number and crypt multiplicity of ACF enumerated. Macroscopic tumors were evaluated at week 20. Total ACF were not different between groups. Average crypt multiplicity and medium (4-6 crypts/focus) and large (> or = 7 crypts/focus) ACF were greater in CHA-CHA and CHA-CON compared with CON-CON and CON-CHA (p < 0.01). Transient exposure to CHA (CHA-CON) was sufficient to induce development of ACF with an accelerated growth phenotype and elicit a tumor-enhancing effect. CHA-CHA had the highest tumor incidence (82.8%, p < 0.05) followed by CHA-CON (56.7%, p < 0.05), and tumor multiplicity and number of tumors per rat in CHA-CON were similar to CHA-CHA (2.29 and 1.3 versus 2.33 and 1.9, respectively). Delayed intervention with CHA (CON-CHA) produced a tumor outcome similar to CON-CON (31 and 30%, respectively), it did not enhance colonic tumor incidence. Taken collectively these results suggest CHA was effective in enhancing colon carcinogenesis during early phases and ineffective in post-initiation phases.     

Senna and the formation of aberrant crypt foci and tumors in rats treated with azoxymethane.

Chronic use of anthraquinone laxatives has been blamed for the induction of habituation and the development of colonic cancer, but there are no definitive studies which have demonstrated this. To evaluate the carcinogenic potential of anthraquinones, the effect of long-term senna pod extract (SE) treatment on either healthy rats or rats treated with an initiating tumor agent (azoxymethane--AOM) has been studied. SE (30 and 60mg/kg), administered for 110 weeks, did not induce the development of aberrant crypt foci (ACF) and tumors in healthy rats. The development of ACF and tumors in rats treated with AOM were significantly reduced by SE (30 and 60 mg/kg). These results suggest that a chronic SE use does not predispose to colon cancer. By contrast, SE might exert an anti-tumoral activity on rat colon carcinogenesis.     

Chemopreventive effects of coffee bean and rice constituents on colorectal carcinogenesis

Polyphenolic compound chlorogenic acid (CGA) known to be much contained in coffee beans was found to have a regressive effect on induced aberrant crypt foci (ACF) as well as on development of ACF in azoxymethane (AOM)-induced colorectal carcinogenesis in rats. Rice germ and gamma-aminobutyric acid-enriched defatted rice germ inhibited AOM-induced ACF formation and colorectal carcinogenesis in rats. Ferulic acid (FA) also known to be contained in coffee beans and rice prevented AOM-induced ACF formation and intestinal carcinogenesis in rats. Both of food factors, coffee and rice may be of benefit to prevention of human colorectal cancers.     

Nitric Oxide Synthase Inhibition Promotes Carcinogen-Induced Preneoplastic Changes in the Colon of Rats

l-Arginine is metabolized either to polyamines through arginase and ornithine decarboxylase (ODC) activities or to citrulline and nitric oxide (NO, nitrogen monoxide) through the NO synthase (NOS) pathway. Polyamine levels and ODC activity are high in tumor cells. The aim of this study was to test whether N(G)-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NOS, modulates colon carcinogenesis. Adult male Wistar rats were treated with azoxymethane (AOM, 15 mg/kg ip), a chemical carcinogen, once a week for 2 weeks. One week after the second injection the rats were randomly divided into two groups. One group (n = 8) received l-NAME (10 mg/kg body wt/day) in drinking water. The control group (n = 8) received tap water. After 5 weeks, the rats receiving l-NAME showed enhanced mean basal arterial blood pressure, decreased heart rate, and a significant decrease of the cGMP content in the colonic mucosa. In both groups, AOM induced the formation of colonic aberrant crypt foci (ACF). In l-NAME-treated rats, the number of ACF was higher than in controls by 47%. ODC activity was enhanced by 11-fold. S-Adenosyl-methionine-decarboxylase activity and putrescine concentration were significantly increased in the colonic mucosa of l-NAME-treated rats. The data suggest that l-NAME promotes carcinogen-induced preneoplastic changes in the colon by inhibiting NOS activity and by stimulating polyamine biosynthesis.     

Citrus limonoids obacunone and limonin inhibit azoxymethane-induced colon carcinogenesis in rats

Obacunone and limonin are bitter limonoids in citrus. Their modifying effects on the development of aberrant crypt foci (ACF), the activity of detoxification enzymes, glutathione S-transferase (GST) and quinone reductase (QR), and cell proliferation activity were investigated in male F344 rats treated with azoxymethane (AOM). Obacunone and limonin were administered in the diet, during the initiation (for 4 weeks) or postinitiation phase (for 4 weeks) of AOM-induced tumorigenesis. Feeding of obacunone and limonin (0.02% or 0.05%) caused significant reduction (55-65% by "initiation" feeding and 28-42% by "postinitiation" feeding) in the yield of ACF. The ability to reduce the proliferating cell nuclear antigen-labeling index in crypts and correlated well with the prevention of ACF. In a subsequent long-term experiment (38 weeks), in which rats were initiated with AOM and fed 0.05% obacunone or 0.05% limonin during the initiation or post-initiation phase, both compounds in diet caused significant reduction (65%-92% inhibition) in the incidence of colonic adenocarcinoma. Thus, citrus bitter limonoids obacunone and limonin possess chemopreventive effects on chemically induced rat colon carcinogenesis.     

Blueberry husks and probiotics attenuate colorectal inflammation and oncogenesis, and liver injuries in rats exposed to cycling DSS-treatment

Long-term colonic inflammation promotes carcinogenesis and histological abnormalities of the liver, and colorectal tumours frequently arise in a background of dysplasia, a precursor of adenomas. Altered colonic microbiota with an increased proportion of bacteria with pro-inflammatory characteristics, have been implicated in neoplastic progression. The composition of the microbiota can be modified by dietary components such as probiotics, polyphenols and dietary fibres. In the present study, the influence of probiotics in combination with blueberry husks on colorectal carcinogenesis and subsequent liver damage was evaluated.Colorectal tumours were induced in rats by cyclic treatment with dextran sulphate sodium (DSS). Blueberry husks and a mixture of three probiotic strains (Bifidobacterium infantis DSM 15159, Lactobacillus gasseri, DSM 16737 and Lactobacillus plantarum DSM 15313) supplemented a basic diet fortified with oats. The condition of the rats was monitored using a disease activity index (DAI). A qualitative and quantitative histological judgement was performed on segments of distal colon and rectum and the caudate lobe of the liver. The formation of short-chain fatty acids, bacterial translocation, the inflammatory reaction and viable count of lactobacilli and Enterobaceriaceae were addressed.Blueberry husks with or without probiotics significantly decreased DAI, and significantly reduced the number of colonic ulcers and dysplastic lesions. With a decreased proportion of blueberry husk in the diet, the probiotic supplement was needed to achieve a significant decrease in numbers of dysplastic lesions. Probiotics decreased faecal viable count of Enterobacteriaceae and increased that of lactobacilli. Blueberry husks with or without probiotics lowered the proportion of butyric acid in distal colon, and decreased the haptoglobin levels. Probiotics mitigated hepatic injuries by decreasing parenchymal infiltration and the incidence of stasis and translocation. The results demonstrate a dietary option for use of blueberry husks and probiotics to delay colonic carcinogenesis and hepatic injuries in the rat model.     

Modulatory efficacy of hesperetin (citrus flavanone) on xenobiotic-metabolizing enzymes during 1,2-dimethylhydrazine-induced colon carcinogenesis

Colorectal cancer is the second leading cause of cancer death worldwide with diet playing a prominent role in disease initiation and progression. Diet and nutrition play an important role during this multistep colon carcinogenic process. We have investigated the modulatory efficacy of hesperetin on aberrant crypt foci (ACF) and xenobiotic-metabolizing enzymes on 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis. Male albino Wistar rats were randomly divided into six groups. Group 1 served as control, received modified pellet diet and group 2 rats received 20 mg/kg body weight of hesperetin p.o. every day. Groups 3-6 rats were given subcutaneous injections of 1,2-dimethylhydrazine (20 mg/kg body weight) once a week for 15 weeks to induce ACF in the colon. In addition, rats in group 4 received hesperetin as in group 2 orally for the first 15 weeks (initiation), group 5 rats received hesperetin as in group 2 after the last injection of DMH and continued till the end of the experimental period (post-initiation). Group 6 received hesperetin as in group 2 throughout the entire period of 32 weeks. DMH exposure showed high incidence (90%) of ACF (280 ± 24.5 aberrant crypt/colon) and dysplastic ACF, elevated activities of phase I enzymes and reduced the activities of phase II enzymes in the liver and colonic mucosa of colon cancer bearing rats. Hesperetin supplementation significantly reversed these effects, the effect being more pronounced in group 6 rats (hesperetin supplemented throughout the study period).These findings suggest that hesperetin can significantly reduce the formation of preneoplastic lesions and effectively modulate the xenobiotic-metabolizing enzymes in rats.     

Protective role of luteolin in 1,2-dimethylhydrazine induced experimental colon carcinogenesis

The aim of the present study was to unravel the chemopreventive effect of luteolin on bacterial enzymes such as beta-glucuronidase and mucinase in a colon carcinogenesis model induced by 1, 2-dimethyl hydrazine (DMH). Twenty mg/kg body weight of DMH were administered subcutaneously once a week for the first 15 weeks and then discontinued. Luteolin (0.1, 0.2, or 0.3 mg/kg body weight/everyday (p.o.) was administered in a dose dependent manner at the initiation and also at the post-initiation stages of carcinogenesis to DMH treated rats. The animals were sacrificed at the end of 30 weeks. Colon cancer incidence and the activities of bacterial enzymes beta-glucuronidase (in the proximal colon, distal colon, intestines, liver and colon contents) and mucinase (colon and fecal contents) were significantly increased in DMH -treated rats compared to the control rats. On luteolin administration, colon cancer incidence, number of tumors per rat and the activities of beta-glucuronidase and mucinase, were significantly decreased both in the initiation and post-initiation stages of colon carcinogenesis dependent on the three different doses given. The increase in beta-glucuronidase activity may augment the hydrolysis of glucuronide conjugates, liberating toxins, while the increase in the mucinase activity may enhance the hydrolysis of the protective mucins in the colon. Thus our results demonstrate for the first time that luteolin, a dietary flavonoid, exerts chemopreventive and anticarcinogenic effects against DMH induced colon cancer.     

Significance and role of early-lesions in experimental colorectal carcinogenesis

Preneoplastic or precancerous lesions in the large bowel have attracted much attention, and aberrant crypt foci (ACF) topographically identified in the colonic mucosa have found application as effective endpoint lesions for detection of chemopreventive agents as well as carcinogenic risk assessment of environmental agents. While many ACF are regarded as hyperplastic in nature, lacking the potential lesion to give rise to neoplasia, a subset termed dysplastic ACF, or newly identified "mucin depleted foci (MDF)", and "beta-catenin accumulated crypts (BCAC)" are suggested to be more reliably related to colorectal tumorigenesis in rodents. ACF and MDF can be visualized on the surface of colonic mucosa and BCAC were recently identified by our laboratory in rodents en face in cross sections. In particular, BCAC having a similar pattern of beta-catenin gene mutation to that observed in colonic carcinomas appear to be direct precursors. This review provides a review and discussion of the relevant literature relative to early lesions in colorectal carcinogenesis.     

Effects of red meat and fiber in high fat diet on activities of sphingomyelinase,ceramidase and caspase-3 in rat colonic mucosa

Red meat and fiber rich foods are the dietary factors most consistently related to colon carcinogenesis. Although several components in these dietary sources may contribute, the biochemical mechanism by which red meat and fiber affect colorectal carcinogenesis has not yet been established. Sphingomyelin metabolism is a novel signal transduction pathway that may have an impact on colonic tumorigenesis. The present study investigated the activity changes of sphingomyelinase (SMase), ceramidase and caspase-3 in colonic mucosa of rats fed on a high fat control diet, the control diet with beef and the control diet with fiber (cellulose). After a three week feeding period the colonic mucosa were scraped and homogenized and enzyme activities were determined. The fiber diet significantly increased the activities of neutral and acid SMases but had no effect on those of alkaline SMase and neutral ceramidase. The beef diet, on the other hand, significantly reduced neutral ceramidase activity, but had no effect on the activities of any SMase. In addition, the beef diet significantly reduced and the fiber diet increased caspase-3 activity in the colonic mucosa when compared with the control diet. The changes of caspase-3 activities were abolished by preincubating the samples with caspase-3 inhibitor. No significant changes of intestinal alkaline phosphatase could be found among the three dietary groups. In conclusion, fiber and red meat in the high fat diet affected in an opposite way the enzymes responsible for sphingomyelin metabolism and apoptosis in the colon. The effects may have implications in colorectal tumorigenesis.     

Lipid peroxidation and activity of antioxidant enzymes in diabetic rats

We hypothesized that oxygen free radicals (OFRs) may be involved in pathogenesis of diabetic complications. We therefore investigated the levels of lipid peroxidation by measuring thiobarbituric acid reactive substances (TBARS) and activity of antioxidant enzymes [superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT)] in tissues and blood of streptozotocin (STZ)-induced diabetic rats. The animals were divided into two groups: control and diabetic. After 10 weeks (wks) of diabetes the animals were sacrificed and liver, heart, pancreas, kidney and blood were collected for measurement of various biochemical parameters. Diabetes was associated with a significant increase in TBARS in pancreas, heart and blood. The activity of CAT increased in liver, heart and blood but decreased in kidney. GSH-Px activity increased in pancreas and kidney while SOD activity increased in liver, heart and pancreas. Our findings suggest that oxidative stress occurs in diabetic state and that oxidative damage to tissues may be a contributory factor in complications associated with diabetes.     

Citrus nobiletin inhibits azoxymethane-induced large bowel carcinogenesis in rats

The inhibitory effects of dietary feeding of citrus nobiletin on azoxymethane (AOM)-induced rat colon carcinogenesis using a long-term bioassay were investigated. Five-week old male F344 rats were initiated with two weekly subcutaneous injections of AOM (20 mg/kg bw) to induce colonic tumors. They were also given the diets containing 0.01% or 0.05% nobiletin for 34 weeks, starting one week after the last dosing of AOM. At the end of the study, the incidence of colonic adenocarcinoma were 67% in the AOM alone group, 55% in the AOM-->0.01% nobiletin group, 35% (p<0.05) in the AOM-->0.05% nobiletin group. Also, nobiletin feeding reduced the cell-proliferation activity, increased the apoptotic index, and decreased the prostaglandin E2 content in colonic adenocarcinoma and/or colonic mucosa. These findings might suggest that citrus nobiletin has chemopreventive ability against AOM-induced rat colon carcinogenesis.     

Suppressive effect of an inducible nitric oxide inhibitor, ONO-1714, on AOM-induced rat colon carcinogenesis.

The expression of inducible nitric oxide synthase (iNOS) is markedly elevated in rat colon cancers induced by azoxymethane (AOM). In addition, iNOS can be detected in most adenomas and dysplastic aberrant crypt foci (ACF), suggesting that iNOS plays an important role in colon carcinogenesis. In the present study, the effect of an iNOS inhibitor, ONO-1714 ((1S,5S,6R,7R)-7-chloro-3-imino-5-methyl-2-azabicyclo[4.1.0] heptane hydrochloride), on AOM-induced rat colon carcinogenesis was investigated. Male F344 rats were treated with 15 mg/kg body weight of AOM once a week, for 2 weeks. ONO-1714 was given to the rats at doses of 10, 20, 50, and 100 ppm in diet for 4 weeks from the day before the first carcinogen treatment. The number of AOM-induced ACF in the rats receiving 10, 20, 50 and 100 ppm ONO-1714 were 94, 73 (P < 0.05), 71 (P < 0.005), and 53% (P < 0.0005), respectively, of the control value. Moreover, the mean number of aberrant crypts per focus was significantly lowered in 100 ppm ONO-1714 group (P < 0.05). Then, the effects of long-term treatment (32 weeks) with 50 and 100 ppm ONO-1714 on AOM-induced colorectal tumor development were examined. Although incidences and multiplicities of colon tumors did not significantly differ among the groups, number of tumors developing in the middle part of colon were reduced with both 50 and 100 ppm doses (P < 0.05). Furthermore, colon tumor volume tended to be decreased by ONO-1714 treatment, and the number of colon tumors more than 3mm in diameter was significantly lowered in the 100 ppm ONO-1714 group (P < 0.01). These results suggest that iNOS plays roles in both early and late stages of colon carcinogenesis.     

Antioxidant enzyme alterations in experimental and clinical diabetes

Previous studies from our laboratory have demonstrated the presence of complex alterations in the activities of antioxidant enzymes in various tissues of rats with streptozotocin (STZ)-induced diabetes. In the present investigation, it is shown that rats made diabetic with alloxan (ALX), an agent differing from STZ both chemically and in its mechanism of diabetogenesis, show virtually identical tissue antioxidant enzyme changes which, as is the case with STZ, are preventable by insulin treatment. The finding that the patterns of antioxidant enzyme alterations in chemically-induced diabetes are independent of the diabetogenic agent used and the presence of similar abnormalities in tissues of spontaneously diabetic (BB) Wistar rats (particularly when diabetic control is less than optimal) suggest that the changes observed are a characteristic feature of the uncontrolled diabetic state and that these may be responsible for (or predispose to) the development of secondary complications in clinical diabetes. Comparative studies involving red cells of diabetic rats and human diabetics revealed a number of common changes, namely an increase in glutathione reductase activity, a decreased susceptibility to oxidative glutathione depletion (which was related to the presence of hyperglycemia) and an increased production of malondialdehyde (an indirect index of lipid peroxidation) in response to in vitro challenge with hydrogen peroxide. In the diabetic patients, the extent of this increase in susceptibility of red cell lipids to oxidation paralleled the severity of diabetic complications. Our results suggest that increased (or uncontrolled) oxidative activity may play an important role in the pathogenesis of complications associated with the chronic diabetic state.This work was supported by grants from the British Columbia Health Care Research Foundation and the Canadian Diabetes Association.     

Regulation of enzymes of glucose metabolism and lipogenesis in diabetic rat liver by thyroid hormones

Experimental diabetes in rats is associated with a degree of hypothyroidism. Hepatic enzymes involved in carbohydrate and lipid metabolism were estimated in control (untreated), control +T3 treated, alloxan diabetic and alloxan diabetic + T3-treated rats. The key glycolytic enzymes, phosphofructokinase and pyruvate kinase, were decreased in activity in diabetes and unchanged by further treatment with T3. In contrast, certain enzymes involve in lipogenesis, ATP-citrate lyase 'malic' enzyme and 6-phosphogluconate dehydrogenase, which were decreased in activity in diabetes, were increased to, or above, control values when diabetic rats were treated with T3. It is suggested that T3 deficiency may play a role in the decrease in enzyme activities observed in experimental diabetes, in particular, some enzymes associated with lipogenesis and the provision of NADPH.