Biomedical subjects

Rui-Dong Duan

Publications and source records attributed to Rui-Dong Duan.

28 records · Page 2Linked to original sources

PubMed2002

In vitro effects of fat, FA, and cholesterol on sphingomyelin hydrolysis induced by rat intestinal alkaline sphingomyelinase.

Dietary sphingomyelin (SM) may have regulatory effects on cell proliferation and tumorigenesis in the colon. Alkaline sphingomyelinase (SMase) is the major enzyme responsible for hydrolysis of SM in the gut. Previously we purified the enzyme and showed that the presence of glycerophospholipids inhibited SM hydrolysis induced by alkaline SMase in vitro. In the present work, we studied the effects of TG, DG, FA, ceramide, and cholesterol on SM hydrolysis catalyzed by purified alkaline SMase. The results showed that both TG (triolein and tristearin) and DG (1,2-dioleoyl-sn-glycerol and 1,2-distearoyl-rac-glycerol) inhibited the activity of alkaline SMase. 1-Monooleoyl-rac-glycerol, 1-monostearoyl-rac-glycerol, stearic acid, oleic acid, linoleic acid, linolenic acid, and arachidonic acid stimulated the activity of alkaline SMase at 0.4-0.8 mM concentrations but inhibited the enzyme at higher concentrations. There was no difference between the effects induced by saturated and unsaturated FA. A short-chain FA such as lauric acid had a stronger stimulatory effect at low concentrations and weaker inhibitory effect at high concentrations than long-chain FA. Choosing linoleic acid as an example, we found that FA had similar effects on both alkaline SMase and neutral SMase. Cholesterol and ceramide when mixed with FA to increase its solubility in bile salt micelles inhibited SMase activity. In conclusion, glycerides, FA, ceramide, and cholesterol influence SM hydrolysis catalyzed by intestinal alkaline SMase. The presence of lipids in the diet may thus influence the course of SM digestion in the gut and thereby the exposure of colon to SM metabolites.

Animals↗

PubMed2002

Boswellic acids trigger apoptosis via a pathway dependent on caspase-8 activation but independent on Fas/Fas ligand interaction in colon cancer HT-29 cells.

Boswellic acids are the effective components of gum resin of Boswellia serrata, which has anti-inflammatory properties. Recent studies on brain tumors and leukemic cells indicate that boswellic acids may have antiproliferative and apoptotic effects with the mechanisms being not studied in detail. We studied their antiproliferative and apoptotic effects on colon cancer cells and the pathway leading to apoptosis. HT-29 cells were treated with beta-boswellic acid (BA), keto-beta-boswellic acid (K-BA) and acetyl-keto-beta-boswellic acid (AK-BA), respectively. Apoptosis was determined by flow cytometry, by cytoplasmic DNA-histone complex and the activity of caspase-3. The cleavage of poly-(ADP-ribose)-polymerase (PARP) and expression of Fas were examined by western blot. Specific caspase inhibitors, polyclonal Fas antibody, and antagonistic Fas antibody ZB4 were employed to elucidate apoptotic pathways. DNA synthesis and cell viability were examined. Both K-BA and AK-BA increased cytoplasmic DNA-histone complex dose-dependently and increased pre-G(1) peak in flow cytometer analysis, with the effects of AK-BA being stronger than K-BA. BA only increased the formation of DNA-histone complex at a high concentration. K-BA and AK-BA increased caspase-8, caspase-9 and caspase-3 activities accompanied by cleavage of PARP. The effects of AK-BA on formation of cytoplasmic DNA histone and on caspase-3 activation were 3.7- and 3.4-fold, respectively, more effective than those induced by camptothecin. The apoptosis induced by AK-BA was inhibited completely by caspase-3 or caspase-8 inhibitor and partially by caspase-9 inhibitor. ZB4 blocked exogenous Fas ligand-induced apoptosis, but had no effect on AK-BA-induced apoptosis. AK-BA had no significant effect on expression of Fas. Apart from apoptotic effect, these acids also inhibited [(3)H]thymidine incorporation and cell viability to different extent. In conclusion, boswellic acids, particularly AK-BA and K-BA have antiproliferative and apoptotic effects in human HT-29 cells. The apoptotic effect is mediated via a pathway dependent on caspase-8 activation but independent of Fas/FasL interaction.

Anti-Inflammatory Agents↗

PubMed2002

Chronic colitis is associated with a reduction of mucosal alkaline sphingomyelinase activity.

BACKGROUND AND AIMS: The hydrolysis of sphingomyelin (SM) generates key molecules regulating cell growth. Animal cancer studies support an inhibitory role for this pathway in the malignant transformation of the colonic mucosa. The activity of a specific intestinal alkaline sphingomyelinase (SMase), which hydrolyzes SM, is reduced in colorectal tumors. In this study we measured alkaline SMase activity in patients with longstanding colitis and assessed if a reduction can be used as a marker in surveillance of high risk patients. METHODS: Alkaline SMase activity was measured in 139 colonic biopsies from 34 patients with longstanding, extensive colitis and from 11 controls. Fifteen patients had earlier diagnosis of dysplasia or DNA aneuploidy. Alkaline SMase activity was related to histologic dysplasia and DNA aneuploidy assessed by flow cytometry, patient age, and duration of disease. RESULTS: Alkaline SMase activity was significantly lower in the patient group with and without dysplasia compared with controls (p = 0.006). In biopsies, an association was not found between alkaline SMase activity, dysplasia, or DNA ploidy. However, alkaline SMase activity decreased with age both in patients and controls (p = 0.008). CONCLUSIONS: Reduction of alkaline SMase activity seen in colorectal cancer and adenomas is also present in patients with chronic colitis. It is not complementary to dysplasia or DNA-aneuploidy in the identification of high risk patients. The age-associated decrease of alkaline SMase activity seems to be a general phenomenon indicating premature senescence of the mucosa in longstanding colitis.

Adenoma↗

PubMed2002

Purification, characterization, and expression of rat intestinal alkaline sphingomyelinase.

Intestinal alkaline sphingomyelinase (SMase) has physiological roles in the digestion of sphingomyelin (SM) and clinical implications in colonic carcinogenesis. In the present work, the enzyme from rat has been purified 1,589-fold with 11% recovery by elution of the intestine with bile salt, precipitation of the proteins by acetone, and several types of chromatographies. Its molecular mass was 58 kDa and optimal pH was 9 to 9.5. Under the optimal conditions, the V(max) was 930 micromol/h/mg and K(m) was about 1.25 mM. The enzyme could hydrolyze phosphatidylcholine at pH 7.4 in the presence of Ca2+; the rate was about 8% of that for SM. The activity against SM was dependent on bile salt. Taurine conjugated bile salts were much more effective than glycine conjugated ones, and the most effective bile salts were taurocholate and taurochenodeoxycholate. 3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) and Triton X100 (TX100) had no stimulatory effects. Unlike neutral SMase, intestinal alkaline SMase was not Mg2+ dependent, not inhibited by EDTA, and not inhibited by glutathione. The enzyme was stable during incubation with temperatures up to 50 degree C and in pHs from 7 to 10. Trypsin and chymotrypsin had no effects on its activity, and 10 mM dithiothreitol reduced its activity by 25%. A specific antibody against the enzyme was developed, and Western blot showed that the enzyme was expressed in the intestine but not in other organs. In conclusion, we purified a potentially important SMase in the intestine with several properties different from neutral SMase.

Animals↗

PubMed2002

Hepatic cirrhosis increases sensitivity of kidney to endotoxin in rats.

BACKGROUND: Renal failure in cirrhotic patients is a severe complication and endotoxemia might be involved. We investigated the effect of endotoxin on renal function of cirrhotic rats and the potential protective role of N-acetylcysteine (NAC). MATERIAL/METHODS: Hepatic cirrhosis was generated in a rat model by carbon tetrachloride. Both cirrhotic and normal rats were insulted by endotoxin intravenously, while another cirrhotic group was pre-treated with NAC. Blood urea nitrogen (BUN) and creatinine were assayed eight hours later. The changes in serum tumor necrosis factor-a (TNF-a) were assayed by ELISA. The histological changes in the kidney were observed after hematoxylin and eosin staining. RESULTS: Endotoxin increased the BUN and creatinine levels in both normal and cirrhotic rats, with a much higher elevation in the latter group. TNF-a concentration was also increased by endotoxin; the changes are positively correlated with BUN and creatinine. NAC pretreatment significantly attenuates the effects of endotoxin on BUN, creatinine and TNF-a levels in cirrhotic rats with no improvement in systemic toxicity symptoms. There were no obvious histological changes in the kidney of these animals. CONCLUSIONS: Hepatic cirrhosis increased the sensitivity of renal function to endotoxemia, which may be protected by NAC.

Acetylcysteine↗

PubMed2002

Keto- and acetyl-keto-boswellic acids inhibit proliferation and induce apoptosis in Hep G2 cells via a caspase-8 dependent pathway.

Boswellic acids are the compounds isolated from the gum resin of Boswellia serrata and have been used for the treatment of inflammatory diseases for many years in the countries of the east. Recently, a few studies showed that the acids may have anti-cancer effect on leukemia and brain tumours. We investigated the apoptotic and anti-proliferative effects of two types of boswellic acids, keto-beta-boswellic acid and acetyl-keto-beta-boswellic acid, on liver cancer Hep G2 cells. After treating the cells with the boswellic acids, cell proliferation, DNA synthesis, and apoptosis were analysed. The activities of caspase-3, -8 and -9 were assayed. To explore the apoptotic pathway, specific caspase inhibitors were employed. It was found that boswellic acids decreased cell viability and [3H]thymidine incorporation, checked the cells in the G1 phase, and increased percentage of sub-G1. Boswellic acids strongly induced apoptosis accompanied by activation of caspase-3, -8 and -9. The apoptosis was blocked completely by caspase-8 or caspase-3 inhibitor, but inhibited partly by caspase-9 inhibitor. However, these caspase inhibitors did not show any effect on the alternations of cell viability caused by boswellic acids. In conclusion, boswellic acids have anti-proliferation and anti-cancer effects on Hep G2 cells. The apoptotic effect is mediated by a pathway dependent on caspase-8 activation. The acids may be a promising drug for the chemoprevention of liver cancer.

Anticarcinogenic Agents↗

PubMedDate not supplied

Effects of fat, beef and fiber in diets on activities of sphingomyelinase, ceramidase and caspase-3 in rat colonic mucosa.

OBJECTIVE: The present study investigates the activity changes of sphingomyelinase (SMase), ceramidase and caspase-3 in colonic mucosa of rats induced by high fat and red meat diets. METHOD: For a period of 3 weeks, rats were fed protein without fat (control), high fat only, high fat with beef, and high fat with fiber (cellulose) diets. The fat content (22.4%) was constant in the three high fat diets. Then, the colonic mucosae were scraped and homogenized and the activities of SMase, ceramidase and caspase-3 determined. RESULTS: Compared to the control diet, the fat diet and fat with beef diet reduced intestinal alkaline SMase by 80 and 84%, respectively; ceramidase activity by 60 and 92%, respectively, and caspase-3 activity by 40 and 75%, respectively. The activities of acid and neutral SMases were also decreased by fat and fat with beef diets but to a smaller extent than those of alkaline SMase. Supplement of fiber in the fat diet had no effect on the changes of alkaline SMase activity but prevented fat-induced decreases in acid and neutral SMase activities and partially prevented those of ceramidase and caspase-3 activities. The activity of intestinal alkaline phosphatase was not changed by any of the diets. CONCLUSION: Fat, beef and fiber significantly affect the enzymes responsible for sphingomyelin metabolism and apoptosis in the colon. The effects may have implications in colonic tumorigenesis related to dietary factors.

Amidohydrolases↗

PubMedDate not supplied

Sulindac induces apoptosis, inhibits proliferation and activates caspase-3 in Hep G2 cells.

BACKGROUND: It has recently been reported that sulindac has an apoptotic effect on KYN-2 cells, an undifferentiated hepatoma cell line. The present work investigates whether sulindac also has an apoptotic effect on well-differentiated hepatoma cells and what its potential mechanism might be. MATERIALS AND METHODS: Hep G2 cells were treated with sulindac at different concentrations. Apoptosis rate, cell proliferation and 3H-thymidine incorporation were measured. The activities of caspase-3, acid and neutral sphingomyelinase and the changes of sphingomyelin content were also assayed. RESULTS: Sulindac dose-dependently induced apoptosis in Hep G2 cells; both sulindac sulfone and sulfide had similar effects. The apoptosis was accompanied by an increase of caspase-3 activity and a decrease of cell proliferation and 3H-thymidine incorporation. No significant change could be observed for the activity of sphingomyelinase and sphingomyelin content. CONCLUSION: Sulindac induces apoptosis and inhibits proliferation in Hep G2 cells. The effect may be mediated by a pathway related to caspase-3 activation but independent of sphingomyelin metabolism

Anti-Inflammatory Agents, Non-Steroidal↗

PubMedDate not supplied

Ursolic acid inhibits proliferation and stimulates apoptosis in HT29 cells following activation of alkaline sphingomyelinase.

BACKGROUND: Ursolic acid (UA) is a plant component with anti-inflammatory and anti-proliferative properties. Its effect on colon cancer is not clear. We studied the anticancer effects of UA on human colon cancer cells. MATERIALS AND METHODS: HT-29 cells were treated with UA. Cell proliferation was determined by cleavage of WST-1. Apoptosis was assayed by cytosolic DNA-histone complex and caspase activity. Sphingomyelinase and alkaline phosphatase were determined against specific substrates. RESULTS: UA dose-dependently decreased cell proliferation and induced apoptosis, accompanied by activation of caspase 3, 8 and 9. Its antiproliferative effect was stronger than those of sulindac and camptothecin and its apoptotic effect stronger than those of boswellic acid and sulindac. UA selectively increased the activity of intestinal alkaline sphingomyelinase, which occurred before activation of caspases. UA had no effect on alkaline phosphatase activity. CONCLUSION: UA has strong anti-proliferative and apoptotic effects on HT-29 cells. The effects may be mediated by alkaline sphingomyelinase activation.

Alkaline Phosphatase↗

PubMedDate not supplied

Anticancer compounds and sphingolipid metabolism in the colon.

Sphingomyelin metabolism generates anticancer signals such as ceramide and sphingosine that may inhibit cell proliferation, and induce differentiation and apoptosis. Changes of sphingomyelin metabolism are found to be associated with tumorigenesis in various tissues and a particular link between sphingomyelin metabolism and colon cancer has been indicated. The effects of several anticancer drugs on sphingomyelin metabolism have been examined recently and there is an increasing interest in discovering new drugs taking sphingomyelin as a target. The present review outlines the sphingomyelin metabolism pathway, introduces the evidence linking sphingomyelin to colon cancer, and summarizes the anticancer drugs and dietary factors that affect the metabolism of sphingomyelin and, thus, the production of the anticancer messengers in the colon.

Animals↗