Bertram I. Cohen

Radial artery conduits improve long-term survival after coronary artery bypass grafting.

BACKGROUNDnThe second best conduit for coronary artery bypass graft surgery (CABG) is unclear. We sought to determine if the use of a second arterial conduit, the radial artery (RA), would improve long-term survival after CABG using the left internal thoracic artery (LITA) and saphenous vein (SV).nnnMETHODSnWe compared the 14-year outcomes in propensity-matched patients undergoing isolated, primary CABG using the LITA, RA, and SV versus CABG using the LITA and only SV. In all, 826 patients from each group had similar propensity-matched demographics and multiple variables. The primary endpoint was all-cause mortality obtained using the Social Security Death Index.nnnRESULTSnPerioperative outcomes including in hospital mortality (0.1% for the RA patients and 0.2% for the SV patients) were similar. Kaplan-Meier survival at 1, 5, and 10 years was 98.3%, 93.9%, and 83.1% for the RA group versus 97.2%, 88.7%, and 74.3% for the SV group (log rank, p = 0.0011). Cox proportional hazards models showed a lower all-cause mortality in the RA group (hazard ratio 0.72, confidence interval: 0.56 to 0.92, p = 0.0084). Ten-year survivals showed a 52% increased mortality for the SV patients (25.7%) versus the RA patients (16.9%; p = 0.0011). For symptomatic patients, RA patency was 80.7%, which was not different than the LITA patency rate of 86.4% but was superior to the SV patency rate of 46.7% (p < 0.001).nnnCONCLUSIONSnUsing the LITA, SV, and a RA conduit for CABG results in significantly improved long-term survival compared with using the LITA and SV. The use of two arterial conduits offers a clear and lasting survival advantage, likely due to the improved patency of RA grafts. We conclude that RA conduits should be more widely utilized during CABG.

Dietary fat and fatty acids modulate cholesterol cholelithiasis in the hamster.

We tested two hypotheses, i) whether the type and the amount of fat in the diet will affect the formation of cholesterol gallstones in the hamsters, and ii) whether palmitic acid, a major fatty acid component of butterfat, can act as a potentiator of cholesterol cholelithiasis in the hamster. Young, male golden Syrian hamsters (Sasco) were fed a semipurified diet containing casein, corn starch, cellulose and cholesterol (0.3%) to which various types and amounts of fat (butterfat, olive oil, menhaden oil, corn oil) were added. All diets contained 2% corn oil to supply essential fatty acids to the growing hamsters. No deaths or illness occurred during the experiment. Animals fed the semipurified diet plus 4% butterfat (group 1) had a gallstone incidence of 63%. Replacement of butterfat with either olive oil, corn oil or menhaden oil prevented the formation of cholesterol gallstones entirely (groups 2–4). When total butterfat was increased from 4% to 8% (group 8), the incidence of cholesterol gallstones increased to 80%. Substitution of 4% olive oil (group 5), corn oil (group 6), or menhaden oil (group 7) for the additional 4% butterfat significantly reduced gallstones to 35%, 45% and 30%, respectively. The replacement of 4% butterfat with 1.2% palmitic acid gave the highest incidence of cholesterol gallstones (95%). These results suggest that butterfat (and one of its components, palmitic acid) intensifies gallstone formation in this model whereas mono- and polyunsaturated fats act as inhibitors of cholesterol cholelithiasis. A fatty acid, possibly palmitic acid, appears to act as lithogen in our model.

Dietary induction of cholesterol gallstones in hamsters from three different sources.

Cholesterol gallstones were produced in young male, golden Syrian hamsters, obtained from three different suppliers, by administering a nutritionally adequate, semipurified diet for periods of either 5 or 10 weeks. The major components of the lithogenic diet were casein, cornstarch, butterfat, corn oil and 0.3% cholesterol. The hamsters were obtained from Sesco, Harlan Sprague-Dawley (Engle hamster) and Charles River (Lakeview hamster). There were profound differences among the three groups with respect to gallstone formation and cholesterol metabolism: The highest incidence of gallstones occurred in Sesco hamsters, 44.4% and 63.6% after 5 and 10 weeks on the lithogenic diet, respectively. In the Engle hamster, after a 5-week feeding, cholesterol crystals and gallstones were absent. When the feeding period was extended to 10 weeks, cholesterol gallstones were present in 45.5% of the animals. In the Lakeview hamsters, neither gallstones nor cholesterol crystals were found in the gallbladder after a 5-week period. After 10 weeks, cholesterol gallstones were found in only a single hamster. In all groups, the lithogenic diet produced large increases of liver, serum and biliary cholesterol concentrations and increased liver weights. When the animals were fed for 5 weeks, only the bile of Sesco hamsters became supersaturated. Supersaturated bile was induced in all groups after a 10-week feeding of the lithogenic diet with cholesterol saturation ranging from 1.47 to 1.97. These data indicate that it is possible to induce cholesterol gallstones in hamsters by means of a nutritionally adequate, semipurified diet of moderate cholesterol content. The source of the animals appears to be an important variable, because there were significant differences among the hamsters of differing origins, in cholesterol metabolism and rates of gallstone formation.

Palmitic acid enhances cholesterol gallstone incidence in sasco hamsters fed cholesterol enriched diets

In an established hamster model of cholesterol cholelithiasis, a semipurified lithogenic diet containing 4% butterfat and 0.3% cholesterol leads to the production of cholesterol gallstones in only 50–60% of animals after a 6-wk feeding period. The purpose of this study was to investigate whether gallstone incidence could be increased while feeding a nutritionally adequate diet of moderate cholesterol content. The semipurified lithogenic diet was modified as follows: (i) substitution of 1.2% palmitic acid for 4% butterfat, and (ii) varying the amount of dietary cholesterol from 0.0 to 0.3% with either butterfat or palmitic acid as the lipid component of the diet. Substitution of palmitic acid for butterfat produced a significantly higher incidence of cholesterol gallstones (94%vs. 53%). Palmitic acid also raised the incidence of gallstones when added to the 0.1% and 0.2% cholesterol diets as compared to butterfat: 0%vs. 44% and 50%vs. 81%, respectively. Gallstone incidence increased from 0% to nearly 100% when the cholesterol content of the palmitic acid diets was raised from 0.0% to 0.3%, indicating a dose response effect with respect to dietary cholesterol. Hamsters fed cholesterol-free diets did not form gallstones. Increased dietary cholesterol led to increased liver weight associated with a significant increase in liver cholesterol concentration. However, the palmitic acid groups had significantly lower liver cholesterol values than the corresponding butterfat groups. Serum and biliary cholesterol concentrations increased with increasing dietary cholesterol intake, but there were no differences between the butterfat and palmitic acid groups. The cholesterol saturation index increased from 0.56 to 1.32 in the butterfat groups and from 0.56 to 1.30 in the palmitic acid groups upon raising the dietary cholesterol from 0.0 to 0.3%. Biliary total bile acid concentration did not vary significantly within all groups; however, the addition of cholesterol produced an increase in the ratio of chenodeoxycholic acid to cholic acid. It is concluded that in Sasco hamsters the saturated fatty acid, palmitic acid, when substituted for butterfat in a nutritionally adequate lithogenic diet, is capable of increasing gallstone incidence to almost 100% during a 6-wk feeding period.

Hydroxylation of secondary bile acids in the perfused prairie dog liver

Taurolithocholic acid and deoxycholic acid were perfused into isolated prairie dog livers. Taurolithocholic acid was 7α-hydroxylated to form taurochenodeoxycholic acid, whereas deoxycholic acid was conjugated and 7α-hydroxylated to form taurocholic acid. The low concentrations of secondary bile acids observed in prairie dog bile are due, at least in part, to active bile acid 7α-hydroxylase(s) in the liver of these animals.

A hydrophilic bile acid effects partial dissolution of cholesterol gallstones in the prairie dog.

Gallstone formation and dissolution were studied in a prairie dog model of cholesterol (CH) cholelithiasis. Gallstones were induced in 49 prairie dogs by feeding 1.2% CH in a nutritionally adequate semisynthetic diet for 6 wk (period 1). At 6 wk, gallstones had developed in all animals examined. The diets were modified by reducing the amounts of CH to 0.4, 0.2, 0.1 and 0.0% (diets 1–4); hyodeoxycholic acid (HDA; 30 mg/kg/day) was added to these diets (diets 5–8). All animals were fed the modified experimental diets for an additional 8 wk (period 2). At week 14, spontaneous gallstone dissolution had not occurred, even in the groups given no added dietary CH during period 2 (group 4). Addition of HDA to the diet tended to reduce the incidence of biliary CH crystals and the size and number of CH gallstones. Biliary CH remained elevated and the lithogenic indices in all groups were found to be greater than 1.0 at the end of the experiment. Liver and plasma CH levels tended to be lower in the groups fed HDA. In these groups, HDA and 6βHDA became the major biliary bile acids. This study demonstrates that HDA achieved partial dissolution of gallstones in bile supersaturated with CH.

The effect of alfalfa-corn diets on cholesterol metabolism and gallstones in prairie dogs

Cholesterol gallstones were present in prairie dogs fed alfalfa plus corn with and without exogenous cholesterol (0.4%). The diets fed to the animals for eight weeks contained alfalfa plus corn in fixed proportions of 50∶50, 85∶15 and 15∶85 (w/w). At sacrifice, all animals were healthy but had not gained weight; no deaths occurred during the experiment. Cholesterol gallstones were present in all groups. In the absence of exogenous cholesterol, the highest stone incidence was found in the animals which received the lowest fiber (highest corn) diets (alfalfa plus corn, 50∶50, 67%; alfalfa plus corn, 15∶85, 83%). Cholesterol gallstone incidence was 100% when exogenous cholesterol was added to the alfalfa plus corn diets (50∶50 and 15∶85). No pigment gallstones were detected in any animal. Liver and plasma cholesterol concentrations were highest in the animals receiving alfalfa plus corn (15∶85) plus 0.4% cholesterol (4.29 mg/g, and 356 mg/dl, respectively). These values were lowest in animals receiving 85% alfalfa plus 15% corn without cholesterol (2.19 mg/g and 88 mg/dl, respectively). Lithogenic indices were below 1.00 in all groups. Biliary bile acids were mainly amidates of cholic acid and chenodeoxycholic acid, with the former predominating. Thus, gallstones can be formed in prairie dogs in the absence of exogenous cholesterol; gallstone incidence is reduced by dietary fiber.

The preparation of bile acid amides and oxazolines. II. The synthesis of the amides and oxazolines of ursodeoxycholic acid, deoxycholic acid, hyodeoxycholic acid and cholic acid.

Bile acid amides and oxazolines were synthesized by a sequence of steps involving the reaction of the free bile acid with formic acid to yield the formyloxy derivative, preparation of the formyloxy acid chloride, condensation of the acid chloride with 2-amino-2-methyl-1-propanol to give the amide and, finally, cyclization of the amide with thionyl chloride to give the oxazoline. The oxazolines were characterized by physical constants, thin layer and gas-liquid chromatography and identified by elemental analysis and gas-liquid chromatography-mass spectrometry. Some of the bile acid oxazoline derivatives alter the activity of bacterial 7-dehydroxylases in vitro, and inhibit the growth of certain anaerobic bacteria in pure culture.

Distribution of cholesterol among its carriers in the bile of male and female hamsters.

The distribution of cholesterol among its carriers was studied in the bile of male and female hamsters. Sasco hamsters (Sasco Inc., Omaha, NE) were fed a semipurified diet with 0.0% cholesterol and 4% butterfat (group 1, males; group 4, females); a semipurified diet with 0.3% cholesterol and 1.2% plamitic acid (group 2, males; group 5, females); and a semipirified diet with 0.3% cholesterol and 4% safflower oil (group 3, males; group 6, females). At the end of six weeks, gallstones were found only in male hamsters receiving both cholesterol and dietary fat (fatty acid) (incidence of cholesterol stones: 90% in group 2; 22% in group 3). The biliary cholesterol carriers were separated and isolated from the bile of the hamsters by gel filtration chromatography, using the method of Pattinson [Pattinson, N.R., Willis, K.E., and Frampton, C.M. (1991)J. Lipid Res. 32, 205–214]. In those male hamsters that formed cholesterol gallstones, significant amounts of cholesterol were present in the void volume which contained large cholesterol phospholipid vesicles (void volume vesicles) (23% in group 2 and 15% in group 3). Smaller cholesterol/phospholipid vesicles were eluted next (fractions 30–45) and contained 15% of biliary cholesterol in group 2 and 21% in group 3. The remainder of the cholesterol was associated with mixed cholesterol/phospholipid/bile salt micelles. The cholesterol/phospholipid ratio was larger in both the void volume vesicles and small vesicles (2.40 and 1.48 in group 2; 2.56 and 1.33 in group 3, respectively) compared to the micelles (about 0.3 in groups 2 and 3). In contrast, the bile of the female hasmters contained few vesicles (3% small vesciles in group 5) and the cholesterol/phospholipid ratio of these vesicles was lower (0.94). Hamsters fed cholesterol-free diets (groups 1 and 4) had no biliary cholesterol/phospholipid vesilces; and cholesterol was present in micelles. The results suggest that both the gender and the diet of the hamsters affected the distribution of biliary cholesterol between vesicles and micelles. The development of cholelithiasis in this animal model appears to depend on the rapid nucleation of cholesterol-rich phospholipid vesicles in bile.

Dietary fat alters biliary lipid secretion in the hamster

Dietary fat has been found to alter the incidence of cholesterol gallstones in hamsters: butterfat intensifies while safflower oil reduces lithiasis. We now report how dietary fat affects bile flow and biliary lipid secretion in this model. Male hamsters were fed one of three experimental diets: a control diet (containing 0.3% cholesterol); control diet +4.0% butterfat; or control diet +4.0% safflower oil. After three weeks, bile samples were collected via an external biliary fistula. The endogenous bile acid pool was depleted for 120 min followed by increasing rates of taurocholate infusion for 160 min. Basal secretion of biliary lipids was measured during the bile acid depletion period. Basal bile flow and bile acid output were not significantly different in the three groups. Dietary butterfat increased basal cholesterol output compared to the control diet (0.037 vs. 0.025 μmol/min·kg, respectively); safflower oil did not change cholesterol output (0.027 μmol/min·kg). Hamsters fed butterfat or safflower oil secreted more phospholipid (0.171 and 0.178 μmol/min·kg, respectively) than controls (0.131 μmol/min·kg). The cholesterol/phospholipid output ratio of the butterfat group was higher than the safflower oil group (0.220 vs. 0.153, respectively). Effects of dietary fat on several relationships between bile flow and biliary lipid secretion were analyzed by linear regression using the data for the entire bile collection period (bile acid depletion and taurocholate infusion). Butterfat and safflower oil did not change either bile acid dependent or bile acid independent bile flow. Hamsters fed butterfat had a higher linkage coefficient (slope) of cholesterol vs. bile acid output than the safflower oil group (0.023 vs. 0.009, respectively). The linkage coefficient of phospholipid vs. bile acid output of the butterfat group was higher than the controls (0.278 vs. 0.185, respectively). In summary, butterfat induced a high cholesterol and phospholipid secretion with a high cholesterol/phospholipid output ratio; safflower oil induced a high phospholipid secretion with a low cholesterol/phospholipid output ratio. Butterfat and safflower oil have different effects on biliary lipid secretion. These differences in biliary lipid secretion may explain, in part, how butterfat and safflower oil differ in affecting gallstone formation in hamsters.