Comparisons of diet and biochemical characteristics of stool and urine between Chinese populations with low and high colorectal cancer rates.

In an investigation of the roles of diet and stool biochemistry in human colorectal carcinogenesis, 24-hour food, urine, and stool samples were collected from randomly selected participants from two populations with a fourfold difference in colorectal cancer risk: Chinese in Sha Giao, People's Republic of China (low risk), and Chinese-Americans of similar ages in San Francisco County, Calif, in the United States (high risk). The findings supported the hypotheses that colorectal cancer risk is increased by the consumption of high-fat, high-protein, and low-carbohydrate diets and is associated with high levels of cholesterol in stool as well as increased daily outputs of 3-methyl-histidine and malonaldehyde in urine. However, risk does not increase with low stool bulk and low total stool fibers.

Calcium enhances the hemolytic action of bile salts.

The lysis of human erythrocytes by bile salts in buffer containing isotonic saline was dramatically enhanced by the addition of 5-10 mM calcium chloride. All bile acids tested showed this effect, with a marked increase in lysis occurring at 0.75 mM for deoxycholate, 1 mM for chenodeoxycholate, 2.5 mM for ursodeoxycholate and 5.5 mM with cholate in the presence of 10 mM calcium chloride. The effect appeared to be specific for calcium; strontium chloride and magnesium chloride gave no stimulatory effect. The increased lysis of the erythrocytes in the presence of 1 mM deoxycholate and 1-10 mM calcium chloride was not associated with increased uptake of the bile salt by the cells (measured with [14C]deoxycholate). Using erythrocytes previously labelled with [3H]cholesterol, there was no evidence of an enhanced removal of that membrane component in the presence of calcium and deoxycholate, compared to deoxycholate alone. The sensitivity of the cells to the effect of calcium in the presence of 1 mM deoxycholate increased with the length of time of their storage at 4 degrees C. The sensitivity returned to that of fresh cells after incubation at 37 degrees C with 30 mM adenosine plus 25 mM glucose, but this treatment did not further diminish the lysis. Lysis in the presence of 10 mM calcium chloride and 1 mM deoxycholate was partially blocked by increasing the KCl concentration at the expense of NaCl. The maximum effect occurred with a buffer comprising 100 mM KCl/50 mM NaCl. A more dramatic reduction in the lysis followed the incorporation of the calcium chelator, quin2, into the cells. The lysis induced by 1 mM deoxycholate in the presence of calcium was reduced by 80% in quin-2-loaded cells compared to controls. The data suggest that bile acids can promote the influx of calcium into erythrocytes, leading to lysis as a result of the efflux of intracellular potassium and/or the uptake of sodium from the incubation medium. The data further suggest that cellular effects may occur at lower bile acid concentrations than that thought to be required for detergent damage.

Synthesis and release of lipids and lipoproteins by isolated rat jejunal enterocytes in the presence of sodium taurocholate.

Isolated rat jejunal villus and crypt cells prepared by differential scraping and hyaluronidase dispersion were used in the presence of 8 mM sodium taurocholate to study the incorporation of sn-[3H]glycerol-2-monooleate, [1-14C]palmitate, [1-14C]acetate, L-[4,5(n)-3H]leucine and D-[1-14C]glucosamine into cellular and medium lipids and proteins, respectively. The villus cells were capable of an apparently normal biosynthesis of triacylglycerols and phospholipids, as well as of proteins and glycoproteins despite an altered dye permeability and increased release of cytosolic and membrane enzymes. About 20-30% of the newly formed triacylglycerols and about 35% of the newly formed phospholipids were secreted into the medium and were recovered as triacylglycerol-rich particles. Labelled proteins and glycoproteins were also recovered from this fraction. The crypt cells synthesized about one-half as much triacylglycerol and phospholipid as did the villus cells, but secreted little or no labelled lipid into the postincubation medium. The release into the medium of triacylglycerols synthesized by the villus cells was blocked by a pretreatment of the isolated cells with the microtubule disruptors, nocodazole, colchicine and colcemid; by the amino sugar, D-galactosamine; by the inhibitors of protein synthesis, puromycin and cycloheximide, and by the inhibitor of the biosynthesis of phosphatidylcholine, chlorocholine. These results indicate that the secretion of labelled lipids, proteins and glycoproteins by the upper villus enterocytes in the presence of sodium taurocholate is not entirely due to cell breakage and spillage of contents. It is concluded that incubations of isolated villus cells of rat jejunum with mixed micellar solutions containing 8 mM taurocholate are compatible with an apparently normal biosynthesis and secretion of triacylglycerol-rich particles.

Molecular species composition of membrane phosphatidylcholine influences the rate of cholesterol efflux from human erythrocytes and vesicles of erythrocyte lipid.

The efflux of [3H]cholesterol from prelabelled human erythrocytes having modified phosphatidylcholine compositions was measured during 24-h incubations in the presence of unlabelled acceptor liposomes composed of equimolar amounts of egg phosphatidylcholine and cholesterol. The cells were modified by replacement of part of the native phosphatidylcholine with either dipalmitoylphosphatidylcholine, palmitoyloleoylphosphatidylcholine or dilinoleoylphosphatidylcholine catalyzed by phosphatidylcholine-specific transfer protein from bovine liver. The results indicated that the efflux of [3H]cholesterol was faster from erythrocytes in which the dipalmitoylphosphatidylcholine content was increased from 7 to 25% of the total, than from cells enriched in palmitoyloleoylphosphatidylcholine or dioleoylphosphatidylcholine. Incorporation of dilinoleoylphosphatidylcholine to a level of 13% of the total phosphatidylcholine slowed the rate of efflux of [3H]sterol. The phosphatidylcholine replacements produced no significant differences in cholesterol/phospholipid ratio before or after 24 h of incubation with the acceptor egg phosphatidylcholine-cholesterol vesicles. Using vesicles prepared from erythrocyte lipid, modified to reflect the changes in the phosphatidylcholine composition induced in the whole cells, the same influence of composition on the rate of cholesterol exchange was evident. Enhancement of the dipalmitoylphosphatidylcholine content from 7 to 25% of the total phosphatidylcholine pool increased the rate of [3H]cholesterol efflux, while the addition of the same amount of dilinoleoylphosphatidylcholine slowed it compared to controls. The magnitude of the effect was comparable in intact cells and erythrocyte lipid vesicles enriched in dipalmitoylphosphatidylcholine, while the influence of dilinoleoylphosphatidylcholine was more marked in the intact cells. These results demonstrate that changes in the molecular species composition of the phosphatidylcholine pool can influence the rate of exchange of cholesterol but not necessarily the cellular content of sterol in the human erythrocyte. The influence of this phospholipid appears to be expressed independently of the presence of membrane protein or an underlying cytoskeleton.

The rate of uptake and efflux of phosphatidylcholine from human erythrocytes depends on the fatty acyl composition of the exchanging species.

The rate of uptake of radioactive phosphatidylcholine molecules of different fatty acid composition in intact erythrocytes as facilitated by a phosphatidylcholine-specific transfer protein has been studied. When trace amounts of radiolabeled phosphatidylcholine molecules are present in donor vesicles consisting of egg phosphatidylcholine and cholesterol, the transfer of the radiolabeled species depends strongly on their fatty acyl composition: dipalmitoylphosphatidylcholine is transferred at the lowest rate, 1-saturated-2-unsaturated species are transferred faster and the highest rate is observed for dioleoyl phosphatidylcholine. Transfer of the various phosphatidylcholine molecules was measured furthermore using donor systems in which the bulk phosphatidylcholine was varied in its fatty acyl composition. Also in this type of experiment, the transfer protein preferentially stimulated transfer of unsaturated phosphatidylcholine molecules, especially from an environment containing more saturated molecules. Finally, the efflux of labeled phosphatidylcholine from intact erythrocytes to plasma in the absence of the phosphatidylcholine-specific transfer protein was studied and it became clear that in this case the nature of the effused molecules itself, rather than the composition of the bulk lipids, determined the effuse rates. An important conclusion to be drawn from these experiments is that radiolabeled phosphatidylcholine molecules, when used as markers for phospholipid exchange or transfer, should resemble in their fatty acid composition the composition of the bulk lipid in order to provide reliable data on rates and extents of the process studied.

Acyl selectivity in the transfer of molecular species of phosphatidylcholines from human erythrocytes.

This report describes the molecular species composition of phosphatidylcholines (PC) transferred from human erythrocytes to acceptor vesicles composed of cholesterol and single PC species in the presence of PC-specific transfer protein from bovine liver. The compositions of the PC isolated from the vesicles were determined by capillary GLC as the diacylglycerol trimethylsilyl ethers. The cellular PC species appearing in the acceptor vesicles were enriched in unsaturated species and showed a low content of dipalmitoyl PC compared to untreated erythrocytes. This trend was independent of the composition of the PC used to construct the acceptor vesicles and it was possible to determine that the relative rates of efflux of the palmitoyl-containing phosphatidylcholines decreased in the order: palmitoyl-linoleoyl greater than palmitoyl-oleoyl greater than dipalmitoyl and in the stearoyl series, stearoyl-linoleoyl greater than stearoyl-oleoyl. No clear trend was distinguished for the influence of chain-length on the efflux, thus preventing an unambiguous assignment of the order of removal of all species from the cell membrane. Results derived for arachidonoyl-containing species were compromised by evidence for oxidation occurring during incubations at 37 degrees C. To confirm that acyl selectivity was also possible during transfer in the absence of the transfer protein, the efflux of 14C-labeled soya PC and [14C]dipalmitoyl PC from prelabeled erythrocytes was measured using plasma as the acceptor. As predicted by the chromatographic analyses, 14C-labeled soya PC effused up to 10-times faster than [14C]dipalmitoyl PC from the red cell membrane. Thus, the more rapid transfer of unsaturated PC cannot be explained entirely as a specificity of the transfer protein and is consistent with the hypothesis that intermolecular interactions involving PC molecules within the erythrocyte membrane, become weaker with increasing unsaturation. The results suggest a potential role of PC-specific transfer protein as a probe of the nature of PC interactions within biological membranes.

The effect of dietary fiber on glucose and hormone responses to a mixed meal in normal subjects and in diabetic subjects with and without autonomic neuropathy.

We investigated the effects of fiber on responses of blood glucose, serum insulin, gastric inhibitory polypeptide (GIP), and immunoreactive pancreatic glucagon (IRG) to ingestion of mixed meal with and without added fiber (5 g guar and 5 g pectin) in 12 normal, healthy subjects and in 12 age-, sex-, and weight-matched non-insulin-dependent, maturity-onset diabetic subjects (NIDDM). Fiber markedly enhanced glucose tolerance in the normal subjects without a change in insulin or GIP but with a significant reduction in glucagon responses. Fiber also markedly improved glucose tolerance in the NIDDMs without changing insulin or GIP but with a significant reduction in the glucagon responses. The NIDDMs were divided into two groups of six subjects, with and without autonomic neuropathy (AN). In NIDDMs without AN, glucose tolerance was improved by fiber without a change in insulin, IRG, or GIP. In diabetic subjects with AN, glucose tolerance was not improved, although glucagon levels were lowered and insulin and GIP responses were unchanged. It appears, therefore, that fiber improves glucose tolerance by altering factors other than insulin. It seems also that autonomic nervous supply to the gastrointestinal tract is important in mediating the effect.

Glucose-dependent insulin-releasing peptide in noninsulin-dependent maturity-onset diabetes: effects of autonomic neuropathy.

Glucose-dependent insulin-releasing peptide or gastric inhibitory polypeptide (GIP) is released into the circulation after ingestion of a mixed meal and is thought to enhance glucose-induced insulin release. We investigated basal and meal-stimulated GIP secretion in noninsulin-dependent maturity-onset diabetics (MODs). Twelve MODs and 12 healthy normal subjects were studied. Mean (+/- SE) basal plasma GIP concentrations were similar in MODs (297 +/- 34.5 pg/ml) and healthy subjects (305 +/- 29.7 pg/ml). Overnight insulin infusion normalized basal glucose levels in the MODs and induced a slight but insignificant rise in plasma GIP levels in MODs to 362 +/- 40.9 pg/ml; overnight gastric aspiration caused a further slight rise in basal GIP concentration to 392 +/- 56.6 pg/ml. The GIP responses to a mixed meal were significantly impaired at 90-240 min in MODs. The MODs were divided into 2 groups, each with 6 subjects: 1 group with autonomic neuropathy (AN) and the other without. The GIP responses in MODs without AN were similar to those in healthy subjects, but were significantly reduced in MODs with AN at all times after the meal. We suggest that the release of GIP after a meal is dependent upon the integrity of the autonomic nervous system; the mechanism may be related to the loss of autonomic control of gastric emptying or dependence of GIP secretion on autonomic modulation.

Gastric inhibitory polypeptide in acquired pancreatic diabetes: effects of insulin treatment.

Oral glucose tolerance tests were done in eight insulin-requiring pancreatic diabetic patients to study the effect of withdrawal of insulin treatment on gut hormone release. Basal levels of gastric inhibitory polypeptide (GIP), glucagon-like immunoreactivity, and immunoreactive glucagon levels rose on insulin withdrawal, more so in patients on short-acting insulin, and were lowered by insulin treatment. Insulin treatment did not affect the GIP, glucagon-like immunoreactivity, or IRG responses to oral glucose. Improved glucose tolerance was greater in patients receiving soluble insulin than in those receiving lente insulin, and there was a significant positive linear correlation between basal plasma GIP and blood glucose levels in these patients. Therefore, it is suggested that insulin treatment lowers basal hormones levels, possibly via a metabolic effect, whereas the hormone responses to oral glucose may be controlled by several factors unrelated to insulin administration or changes in glucose homeostasis.

Inhibition of exaggerated gastrointestinal glucagon responses in chronic pancreatitis by somatostatin.

Oral glucose administration caused an exaggerated release of cross-reacting gastrointestinal glucagon-like immunoreactivity (GLI) and a slight early rise in immunoreactive glucagon (IRG) concentration in patients with chronic pancreatitis, who have impaired insulin release. Intravenous administration of 200 microgram of somatostatin, followed by infusion of 200 microgram over 2 1/2 h, abolished the GLI and insulin responses, but did not change glucose tolerance. This contrasts with the relatively minor effects of somatostatin on GLI responses in control subjects where the clear deterioration in glucose tolerance may relate to inhibition of insulin release.

Cellular toxicity of fecal water depends on diet.

To determine whether concentrations of potentially toxic lipids in the aqueous phase of human stool are responsive to changes in dietary fat, calcium, and fiber, 20 male volunteers were placed on a high-fat, low-calcium, low-fiber or a low-fat, high-calcium, high-fiber diet for 4 days. To assess toxicity of the fecal fractions, we examined the ability of fecal supernatants to lyse human erythrocytes. Bile acid concentrations in fecal water from the low-fat group were reduced significantly from 180 +/- 60 microM to 100 +/- 70 microM; in the high-fat group, increased from 190 +/- 60 microM to 250 +/- 100 microM. Erythrocyte lysis was 76% for the high-fat group, 37% for the low-fat group. There was a significant weak correlation between aqueous bile acid concentration and cell lysis. Results suggest that diet can influence concentrations of detergents in the aqueous phase of human stool and the potential toxicity of this fraction to cell membranes.

Salience of ethnicity in the spontaneous self-concept as a function of one's ethnic distinctiveness in the social environment.

How likely people are to think of themselves in terms of a given personal characteristic is predicted from the distinctiveness postulate that the person, when confronted by a complex stimulus (such as the self), selectively notices and encodes the stimulus in terms of what is most peculiar about it, since these peculiar characteristics are the most informative in distinguishing it from other stimuli. This partial view of the person as an information-encoding machine (one is conscious of oneself insofar as, and in the ways that, one is different) is used to derive four predictions implying that ethnic identity is salient in children's spontaneous self-concepts to the extent that their ethnic group is in the minority in their social milieu at school. Our measure of salience of ethnicity was its being spontaneously mentioned by the children in response to a nondirective "Tell us about yourself" question. All four predictions were confirmed, though for several of the findings there are plausible alternative explanations.

Analysis and structure determination of unsaturated 5 beta - cholanoic acids.

Unsaturated cholanoic acids are known to arise as artifacts of chemical transformation processes and during storage and high-temperature gas liquid chromatography (GLC) of various derivatives of saturated bile acids. Nevertheless, there is evidence for their natural occurrence and isolation under conditions where artifactual formation of unsaturated bile acids would be unlikely. Since structural identification of such compounds is often complicated by a lack of knowledge of their analytical properties, a representative series of monounsaturated cholanoic acids with double bonds in rings A, B and C were prepared by POCl3 and ZnCL2 dehydration of saturated bile acids with selectively blocked hydroxyl functions. The cholenoic acids were indistinguishable from their saturated analogs by thin layer chromatography (TLC) on plain silica gel, but those compounds with sterically exposed double bonds were resolved by AgNO3-TLC, using chloroform/methanol solvent systems. The synthetic 5 beta-cholenoic acids obeyed the general rules of GLC mobility based on the overall shape of the molecule and the number and configuration of the functional groups. Constant retention factors attributable to the double bond were observed for all of the double bond types on several GLC phases, and theoretical retention times could be calculated for combinations of double bonds and functional groups not specifically represented among the synthetic standards. With gas chromatography-mass spectrometry (GC-MS), the unsaturated bile acids gave several characteristic fragments, which, in conjunction with the chromatographic properties of the parent compounds, permitted an unambiguous distinction among different unsaturated acids, and between unsaturated and saturated bile acids of the same number and configuration of functional groups. For complete structural identification of saturated and unsaturated bile acids, capillary GC-MS represents the ideal state of the art, but the less expensive combination of AgNO3-TLC and GLC also can yield much useful information concerning the structure of natural and synthetic 5 beta-cholenoic acids. This study emphasizes the need for special precautions in the isolation and derivatization of bile acids intended for studies of unsaturated components.

Differential uptake of cholesterol and plant sterols by rat erythrocytes in vitro.

The in vitro uptake of radioactively labeled cholesterol and the plant sterol beta-sitosterol has been examined in rat erythrocytes. From mixed micellar solutions containing egg yolk phospholipid and sodium taurocholate, the erythrocytes showed a nonlinear uptake of the two sterols. The uptake leveled off after about 45 min with the attainment of a 1:1 total sterol-to-phospholipid ratio within the cell membrane, as determined on a mass basis. From solutions containing egg yolk phospholipid, or purified egg yolk phosphatidylcholine, a preference for cholesterol over the plant sterol was observed, increasing with time from a cholesterol/beta-sitosterol uptake ratio of unity (the media ratio) to a maximum of 2 after a 60-min incubation. Correction of the data for nonspecifically bound sterol increased the ratio to a maximum of 5 at the 30-min time point. The increase in the cholesterol/beta-sitosterol uptake ratio with time, following an initial nonspecific association, showed that penetration of the plasma membrane by the sterol was required for the selectivity to be expressed. The presence of lysophosphatidylcholine or bovine serum albumin did not exert any noticeable influence over the extent or selectivity of absorption. Replacement of the egg yolk phospholipid with synthetic dipalmitoyl-phosphatidylcholine led to a loss of the sterol selectivity. No evidence was found to support a selective extraction of sterol from the erythrocyte membrane to account for the observed effects, nor was there any sign of a mass accumulation of phospholipid during the incubation. It is suggested that the media phospholipid influences the membrane permeability toward cholesterol and beta-sitosterol.

Sustained feeding or fasting affects levels of glucagon (IRG) in porcine plasma, gut and pancreas.

Arterial glucagon levels are elevated in fed pancreatectomised pigs and the source was sought by measuring the hormone in arterial, portal, hepatic and renal venous blood, and in gut tissues. Pigs which were starved for 48 hours (basal) were compared with sham operated or pancreatectomised pigs which were fed or starved for 7 days post operatively. Feeding of sham operated pigs caused a uniform increase in IRG 3485, while starvation resulted in a decreased portal IRG 7000. Pancreatectomy was associated with a uniform decrease in portal IRG 3485 and increase of IRG 7000 regardless of nutritional status. Hepatic and renal extraction of 23-26% was noted in fed animals (IRG 3485 in sham operated; IRG 7000 in pancreatectomised). In all starved pigs, hepatic and renal extraction were reduced to zero. The gastric and caecal mucosa and the pancreas contained most of IRG 3485. Gastric and caecal levels were increased after feeding of either group of animals, while fasting caused a marked increase in pancreatic IRG 3485 and a decrease in ileal IRG 7000. These studies demonstrate a direct effect of sustained nutritional status upon the distribution of glucagon in plasma and gastro intestinal tissues.