Sigmoidoscopy and Colonoscopy are Inversely Associated with Both Left- and Right-sided Advanced Adenomas

Background: The U.S. Preventive Services Task Force recommends routine colorectal cancer screening starting at age 50; however, evidence is insufficient to recommend one screening method over the other methods. Common colorectal cancer screening methods include fecal occult blood tests (FOBT), sigmoidoscopy, and colonoscopy.

Objective: We examined the association between advanced adenomas, known precursors to colorectal cancer, and history of screening by FOBT, sigmoidoscopy, and colonoscopy.

Methods: We conducted a case-control study of advanced colorectal adenomatous polyps, which included 306 advanced adenoma cases and 2,287 controls without advanced adenomas, aged 24 to 79, who received an index colonoscopy from 1998 to 2007. All participants completed a questionnaire covering screening history and other colorectal cancer risk factors. Participants with polyps underwent a standard pathology review; adenomas ≥10 mm or at with at least 20% villous components were considered advanced adenomas. We used separate logistic regression models to estimate adjusted odds ratios (ORs) and 95% CIs for the associations between advanced adenomas and previous FOBT, sigmoidoscopy, and colonoscopy at least 2 years before the index colonoscopy.

Results: Each screening method was associated with decreased odds of advanced adenomas; however, only associations for sigmoidoscopy and colonoscopy were statistically significant. The OR for advanced adenomas, comparing participants with at least one previous FOBT to those who had never had FOBT, was 0.82 (95% CI: 0.63–1.06); for sigmoidoscopy, OR = 0.59 (95% CI: 0.46–0.77); and for colonoscopy, OR = 0.53 (95% CI: 0.39–0.72). These associations were similar with respect to left- and right-sided advanced adenomas.

Discussion: Our findings suggest colonoscopy and sigmoidoscopy have similar inverse associations with advanced adenomas in both left and right sides of the colon. This is in contrast to studies of colorectal cancer that suggest endoscopy is associated with a decreased risk for tumors of the left but not right side. The discrepancy between our findings and these studies may be explained if right-sided colorectal cancers are more likely to have nonadenoma precursors that are overlooked by screening.

Aerobic exercise training improves the role of high-density lipoprotein antioxidant and reduces plasma lipid peroxidation in type 2 diabetes mellitus

In this study, we analyzed the effect of aerobic exercise training (AET) and of a single bout of exercise on plasma oxidative stress and on antioxidant defenses in type 2 diabetes mellitus (DM) and in healthy control subjects (C). DM and C did not differ regarding triglycerides, high-density lipoprotein cholesterol (HDL-c), insulin, and HOMA index at baseline and after AET. To measure the lag time for low-density lipoprotein (LDL) oxidation (LAG) and the maximal rate of conjugated diene formation (MCD), participants' plasma HDL(2) and HDL(3) were incubated with LDL from pooled healthy donors' plasma. In the presence of HDL(3), both LAG and MCD were similar in C and DM, but only in DM did AET improve LAG and reduce MCD. In the presence of HDL(2), the lower baseline LAG in DM equaled C after AET. MCD was unchanged in DM after AET, but was lower than C only after AET. Furthermore, after AET plasma thiobarbituric acid-reactive substances were reduced only in DM subjects. Despite not modifying the total plasma antioxidant status and serum paraoxonase-1 activity in both groups, AET lowered the plasma lipid peroxides, corrected the HDL(2), and improved the HDL(3) antioxidant efficiency in DM independent of the changes in blood glucose, insulin, and plasma HDL concentration and composition.

The rise of the plasma lipid concentration elicited by dietary sodium chloride restriction in Wistar rats is due to an impairment of the plasma triacylglycerol removal rate

Studies in humans have indicated that dietary salt restriction raises plasma levels of total cholesterol (TC) and triacylglycerols (TAG). In order to explain the mechanisms involved, a rat experimental model was developed consisting of chronic feeding ad libitum isocaloric diets with variable sodium chloride contents. Rates of synthesis of plasma TAG were measured either as the increase of plasma TAG after blocking its removal from plasma by the intra-arterial pulse infusion of Triton-WR 1339, or as the plasma rate of incorporation of [(14)C]-oleic acid [(14)C]-TAG. Plasma TAG removal rate was determined by the intra-arterial pulse infusion of a lipid emulsion. Severe salt restriction increased the plasma concentrations of TAG (71%) and of TC (10%). This result was not due to modification of the rate of synthesis of plasma TAG but was attributed to a 55% slower rate of removal of the TAG-containing lipoproteins. An increased plasma non-esterified fatty acid concentration, probably due to a salt restriction-related insulin resistance, may have impaired the activity of the enzyme lipoprotein lipase.

Diminished rate of mouse peritoneal macrophage cholesterol efflux is not related to the degree of HDL glycation in diabetes mellitus

The efflux of (14)C-cholesterol from mouse peritoneal macrophages mediated by in vivo and in vitro glycation of intact HDL(3) and by HDL(3) apolipoproteins was investigated. Cholesterol-laden cells were incubated a long time with HDL(3) from control subjects (C), poorly controlled diabetes mellitus patients (D) and with HDL C submitted to in vitro glycation (G), as well as with all their respectively isolated apolipoproteins. A diminished cholesterol efflux rate occurred in incubations with intact HDL(3) D but not with intact HDL(3)G or with apoHDL(3)C, G or D. The specific binding of (125)I-HDL(3)G to the cell receptor, obtained upon incubation in the absence and in the presence of excess unlabelled HDL(3), was lower than the control. The role of apoE secretion by cholesterol-laden macrophages on cholesterol efflux was analyzed by incubating apoE knockout and control mice macrophages with HDL C or HDL G: a lower cholesterol efflux was observed from apoE knockout macrophages but glycation of HDL(3) did not influence this process either. The diminished capacity to remove cholesterol by the HDL drawn from diabetic subjects must be attributed to other modifications of the lipoproteins, except for non enzymatic glycation. Thus, events that impair the cell cholesterol removal in diabetes mellitus are multifaceted.

Reverse cholesterol transport in diabetes mellitus

There are epidemiological data and experimental animal models relating the development of premature atherosclerosis with defects of the reverse cholesterol transport (RCT) system. In this regard, the plasma concentrations of the high density lipoprotein (HDL) subfractions, of cholesteryl ester transfer protein (CETP), as well as the activity of the enzyme lecithin-cholesterol acyl transferase (LCAT) play critical roles. However, there has been plenty of evidence that atherosclerosis in diabetes mellitus (DM) is ascribed to a greater arterial wall cell uptake of modified apoB-containing lipoproteins whereas a primary or predominant defect of the RCT system is still a subject of debate. In other words, in spite of the fact that in DM the composition and rates of metabolism of the HDL particles are greatly altered and display a diminished in vitro efficiency to remove cell cholesterol, definitive in vivo demonstration of the importance of this fact in atherogenesis is lacking. Furthermore, the roles played by LCAT and CETP in RCT in DM are difficult to interpret because the in vitro procedures of measurement utilized have either been inadequate, or inappropriately interpreted. Knock-out or transgenic mice are much needed models to investigate the roles of LCAT, CETP, phospholipid transfer protein (PLTP), and of a CETP inhibitor in the development of atherosclerosis of experimental DM.

Dietary medium-chain triacylglycerol prevents the postprandial rise of plasma triacylglycerols but induces hypercholesterolemia in primary hypertriglyceridemic subjects

BACKGROUND

Previous studies showed divergent results concerning the influence of medium-chain triacylglycerol (MCT) on lipoprotein metabolism.

OBJECTIVE

The objective of this study was to compare the effects of MCT and corn oil on plasma lipids in primary hypertriglyceridemic patients.

DESIGN

Ten subjects ate different proportions of corn oil and MCT for 12 wk. The subjects first ate a low-fat diet for 2 wk and during the next 4 wk, corn oil was added as the sole source of fat. Thereafter, for 2-wk periods, the subjects were sequentially fed corn oil and MCT mixed in the following proportions: 3:1, 1:1, and 0:1. Fasting plasma total cholesterol, triacylglycerol, and HDL-cholesterol concentrations were measured at the end of each period. At the end of the 100%-corn oil and of the 100%-MCT periods, subjects were fed a test meal containing the respective oil (40 g fat/m(2) body surface area) and total cholesterol and triacylglycerols were measured at 2-h intervals over 8 h; fasting lipoprotein composition was also measured.

RESULTS

Compared with corn oil, MCT was associated with a higher mean (+/-SD) fasting total cholesterol concentration (6.39 +/- 1.14 compared with 5.51 +/- 0.98 mmol/L, respectively; P < 0. 05); non-HDL-cholesterol concentrations were also higher with MCT (5. 36 +/- 1.11 mmol/L) than with corn oil (4.51 +/- 0.92 mmol/L; P < 0. 005). In response to the liquid test meal, plasma total cholesterol did not change with either diet but triacylglycerols increased with the 100%-corn oil diet.

CONCLUSIONS

MCT prevents the risk of pancreatitis due to postprandial hypertriglyceridemia but has the inconvenience of raising total cholesterol concentrations in primary hypertriglyceridemic subjects.

Lipoprotein desialylation simultaneously enhances the cell cholesterol uptake and impairs the reverse cholesterol transport system: in vitro evidences utilizing neuraminidase-treated lipoproteins and mouse peritoneal macrophages

Desialylation of low density lipoprotein (LDL) brings about accumulation of cholesterol in cultured cells. The influence of the neuraminidase-treated lipoprotein (LP) on the reverse cholesterol transport system was investigated in vitro utilizing very low density lipoprotein (VLDL), LDL, total high density lipoprotein (HDL) and its subfractions, HDL2 and HDL3, isolated from healthy donor plasma and mouse peritoneal macrophages. It was found that LP desialylation significantly: (1) decreased the capacity of total HDL and of HDL2, but not of HDL3, to efflux cellular cholesterol; (2) lowered the cholesterol esterification rate by lecithin:cholesterol acyltransferase (LCAT) without modifying the intrinsic LCAT activity of HDL; (3) increased the cholesteryl ester transfer from HDL to apo B-containing LP mediated by cholesteryl ester transfer protein (CETP); (4) enhanced the uptake by macrophages of cholesterol from HDL and LDL, although the amount of cholesterol taken up by the cells was much greater from the desialylated LDL than from desialylated HDL. Taken together, these in vitro evidences indicate that, in addition to enhancing the cell cholesterol LP uptake, desialylation may contribute to the premature development of atherosclerosis by impairing the reverse cholesterol transport system.

Plasma lipoproteins from patients with poorly controlled diabetes mellitus and "in vitro" glycation of lipoproteins enhance the transfer rate of cholesteryl ester from HDL to apo-B-containing lipoproteins

Alterations in the reverse cholesterol transport system have been described in diabetic mellitus patients in several but not all studies. Furthermore, recently published investigations suggest that a faster "in vitro" transfer rate of cholesteryl ester from high density lipoproteins to apoB-containing lipoproteins could be solely ascribed to variation of the plasma lipoprotein composition and concentration in the diabetic state. The present study analysed the influence of lipoprotein glycation on the cholesteryl ester transfer protein-mediated transfer of esterified cholesterol from high density lipoprotein and its subfractions to lighter density lipoproteins. For this purpose two sets of "in vitro" experiments were carried out utilizing:1) plasma lipoproteins drawn from diabetic and from normal subjects and; 2) normal lipoproteins or partially purified cholesteryl ester transfer protein submitted to "in vitro" glycation. The transfer rate of 14C-cholesteryl ester labelled HDL subfractions to low or very low density lipoproteins was measured in all experiments. After incubations with plasma d > 1.21 g/ml or with purified cholesteryl ester transfer protein, apoB-containing lipoproteins were precipitated with a dextran sulfate/MgCl2 solution. The "in vitro" glycation of the partially purified cholesteryl ester transfer protein, markedly impaired its activity. However, greater transfer rates were observed when lipoproteins from diabetic individuals or the "in vitro" glycated lipoproteins were utilized. This effect was attributed to glycation of the protein component of HDL. In conclusion, lipoprotein glycation elicits an enrichment of the apoB-containing lipoproteins with cholesteryl ester that is likely related to the premature atherosclerosis in patients with poorly controlled diabetes.

The age-related rise of plasma cholesterol in humans is not caused by a cell removal defect of LDL particles: 'in vitro' studies in peripheral mononuclear blood cells

In healthy subjects with a normal body mass index, total plasma cholesterol, low-density lipoprotein (LDL) cholesterol, and apoB lipoprotein levels are higher in older individuals (n = 34) than in younger subjects (n = 43). The two groups studied ranged in age from 60 to 93 years and from 17 to 30 years, respectively. The cholesterol synthesis rates of peripheral mononuclear blood cells from 14C-acetate, total and unesterified cholesterol concentrations in freshly isolated cells, and the rates of uptake of pooled donor LDL, labeled with 125I- or 14C-cholesteryl oleoyl ether, by cells derepressed in a lipoprotein-free medium were similar in both experimental groups. Thus, the rise of LDL cholesterol with age would seem to be likely secondary to the higher rate of very-low-density lipoprotein production, as shown by other investigators.

Major groove (S)-alpha-(N6-adenyl)styrene oxide adducts in an oligodeoxynucleotide containing the human N-ras codon 61 sequence: conformations of the S(61,2) and S(61,3) sequence isomers from 1H NMR

The (S)-alpha-(N6-adenyl)styrene oxide adducts at positions X6 in d(CGGACXAGAAG). d(CTTCTTGTCCG) and X7 in d(CGGACAXGAAG).d(CTTCTTGTCCG), incorporating codons 60, 61 (underlined), and 62 of the human n-ras protooncogene, were examined by 1H NMR. These were the S(61,2) and S(61,3) adducts. Chemical shift perturbations were in the 3'-direction from the sites of adduction; upfield changes associated with the styrene aromatic ring current were noted for S-SOA6 H2 and H1', T16 N3H, H6, and CH3 resonances in the S(61,2) oligomer. In the S(61,3) oligomer, S-SOA7 H1', T16 H1', C15 N4Ha, and H5 shifted upfield. The styrene aromatic rings flipped rapidly on the NMR time scale; under these conditions the ortho and meta aromatic protons were equivalent. A sequence effect, in which the S(61,2) adduct equilibrated between two conformers, while the S(61,3) adduct exhibited only a single conformation, was observed. Potential energy minimization of the S(61,2) adduct major conformation yielded a structure in which the styrene ring was oriented in the 3'-direction and interacted primarily with the complementary strand. For the S(61,3) adduct, 291 restraints were obtained from NOE data at three mixing times using relaxation matrix analysis. The emergent structures refined to an average rms difference of 1.3 A, determined by pairwise analysis. These were compared to NOE intensity data; the calculated sixth root residual index was 9.2 x 10-2 at 250 ms. In the refined structure, the styrene ring was also oriented in the 3'-direction and interacted with the complementary strand. The minor conformation of the S(61,2) adduct was not identified. These results contrasted with the diastereomeric R(61,2) and R(61,3) adducts, which underwent slow ring flips on the NMR time scale and for which small sequence effects involving the minimum energy conformation of the styrene ring were observed.

Major groove (R)-alpha-(N6-adenyl)styrene oxide adducts in an oligodeoxynucleotide containing the human N-ras codon 61 sequence: conformations of the R(61,2) and R(61,3) sequence isomers from 1H NMR

Conformations of (R)-alpha-(N6-adenyl)styrene oxide adducts at positions X6 in d(CGGACXAGAAG).d(CTTCTTGTCCG) and X7 in d(CGGACAXGAAG).d(CTTCTTGTCCG), incorporating codons 60, 61 (underlined), and 62 of the human n-ras protooncogene, were refined from 1H NMR data. These were the R(61,2) and R(61,3) adducts. Chemical shift perturbations were in the 5'-direction from the sites of adduction; large changes were observed for C5 H5 and H6 in the R(61,2) adduct. The styrene moieties were only partially defined by NOE data. Spectral overlap, particularly for the R(61,2) adduct, prevented complete assignments of the aromatic resonances; likewise, there were insufficient data to orient the CH2OH moieties. Ring flips were slow on the NMR time scale. For the R(61,2) adduct 260 restraints were obtained from NOE data at three mixing times using relaxation matrix analysis; for the R(61,3) adduct 230 restraints were obtained. Structures emergent from molecular dynamics/simulated annealing for the R(61,2) adduct converged to average and maximum pairwise rms differences of 1.3 and 1.7 A, respectively, while those for the R(61,3) adduct converged to average and maximum pairwise rms differences of 1.2 and 1.6 A. Sixth root residual indices of 7.5 and 6.8 x 10(-2) were measured between the refined structures and NOE intensities using relaxation matrix calculations for the R(61,2) and R(61,3) adducts, respectively. The styrene rings were in the 5'-direction from the lesion sites in the major groove. The preferred orientation calculated for the R(61,2) adduct placed the styrene ring edgewise and approximately orthogonal to C5, while that calculated for the R(61,3) duplex had the styrene ring approximately orthogonal to the major groove edges of base pairs A6.T17 and R-SOA7.T16.

The effect of eicosapentaenoic acid consumption on human neutrophil chemiluminescence

The effect of eicosapentaenoic acid (EPA) on the inflammatory potential of neutrophils was investigated by supplementing the diets of 12 subjects with 2.16 g of EPA or 12 g of olive oil per day for 4 weeks in a double blind crossover study. Neutrophil function as assessed by luminol enhanced chemiluminescence responses to platelet-activating factor (PAF) and formyl-methionyl-leucyl-phenylalanine (FMLP) was significantly reduced after EPA but not after olive oil consumption in the subjects who consumed EPA first. In contrast, EPA had no significant effect on neutrophil chemiluminescence in the subjects who consumed olive oil first. Dietary supplementation with EPA inhibits neutrophil responses to inflammatory mediators such as PAF while other fatty acids appear to modify the effects of EPA.