Open adhesiolysis is more effective in reducing adhesion reformation than laparoscopic adhesiolysis in an experimental model

BACKGROUND

This study compared adhesion reformation after open and laparoscopic adhesiolysis in a rat model.

METHODS

Adhesions were induced by surgically creating ischaemic buttons on the peritoneal side wall. After 7 days the animals underwent laparoscopy with carbon dioxide insufflation or laparotomy to score and lyse adhesions. Peritoneal tissue and fluid were collected after 24 h in a subset of animals, and adhesion reformation was scored 7 days after lysis in the remainder. Tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI) 1, transforming growth factor (TGF) beta1 and tumour necrosis factor (TNF) alpha mRNA, and total fibrinolytic activity were assessed. The abdomen of non-operated animals was insufflated for 7, 15 or 30 min with carbon dioxide, after which tPA and PAI-1 mRNA and total fibrinolytic activity were measured.

RESULTS

Animals that underwent open adhesiolysis had 60 per cent fewer reformed adhesions than the laparoscopic adhesiolysis group (P < 0.001). There were no differences in tPA activity or tPA, PAI-1 and TNF-alpha mRNA between groups, but TGF-beta1 mRNA levels were significantly increased in the open group. Carbon dioxide insufflation did not affect peritoneal tPA activity.

CONCLUSION

Open adhesiolysis may be more beneficial in minimizing adhesion reformation in the management of adhesion-related complications.

A neurokinin 1 receptor antagonist decreases adhesion reformation after laparoscopic lysis of adhesions in a rat model of adhesion formation

BACKGROUND

Up to 94% of patients experience fibrous adhesions after abdominal surgery, and a significant number of these patients require a second operation for open or laparoscopic lysis of adhesions (LOA). The authors have previously shown that inhibition of the binding of tachykinin ligands to the neurokinin 1 receptor (NK-1R) using the neurokinin 1 receptor antagonist (NK-1RA) CJ-12,255 decreases primary adhesion formation and upregulates the peritoneal fibrinolytic system in a rat model. Whereas most studies have focused on the prevention of primary adhesions, few have addressed adhesion reformation after LOA. This study aimed to determine the effects of NK-1RA administration on adhesion reformation and peritoneal fibrinolytic activity after laparoscopic LOA.

METHODS

Adhesions were induced in 31 rats using our previously described ischemic button model. The rats underwent laparoscopy 7 days later, during which adhesions were scored and lysed followed by administration of the NK-1RA or saline. Then 7 days after LOA, 23 rats were killed and adhesions were scored. Eight rats also were killed 24 h after the LOA to obtain peritoneal tissue and fluid, which were analyzed for tissue plasminogen activator (tPA) mRNA expression and peritoneal fibrinolytic activity by reverse transcriptase-polymerase chain reaction (RT-PCR) and bioassay, respectively.

RESULTS

At laparoscopy, 79% +/- 3% of the buttons formed adhesions. In the saline-administered control animals, 42% +/- 3.2% of the buttons reformed adhesions after LOA (p < 0.05), whereas in the animals that received the NK-1RA, 18.2% +/- 3.5% of the buttons reformed adhesions (p < 0.05). As compared with control animals, NK-1RA administration increased tPA mRNA levels by 38% and fibrinolytic activity sixfold (p < 0.05; 7.0 +/- 2.1 U/ml vs 1.2 +/- 0.54 U/ml).

CONCLUSIONS

When administered during laparoscopic LOA, an NK-1RA significantly upregulates peritoneal fibrinolytic activity and decreases adhesion reformation.

Increased F2 isoprostanes in the acute chest syndrome of sickle cell disease as a marker of oxidative stress

Nitric oxide metabolism is altered during the acute chest syndrome of sickle cell disease. In the presence of oxygen and oxygen-related molecules, nitric oxide can preferentially form the powerful oxidants nitrite, nitrate, and peroxynitrite. We hypothesized that increased oxidative stress may contribute to the pathogenesis of acute chest syndrome and measured F2 isoprostanes, a nonenzymatically generated molecule resulting from free radical catalyzed lipid peroxidation in patients with sickle cell disease in various stages of disease. Plasma samples were obtained from nineteen patients with sickle cell disease during acute chest syndrome (pre- and postexchange transfusion), vasoocclusive crisis, and/or at baseline; 12 normal volunteers served as controls. F2 isoprostanes were measured by gas chromatography/mass spectrophotometry. There was a 9-fold increase in F2 isoprostanes in patients with acute chest syndrome as compared with normal volunteers. There was approximately a 50-60% decline in isoprostanes postexchange transfusion to a level similar to that of patients with sickle cell disease at baseline. There was no difference in isoprostanes between vasoocclusive crisis and patients with sickle cell disease at baseline. Increased oxidative stress, measured by generation of F2 isoprostanes, occurs during acute chest syndrome and may have an important role in the pathogenesis of this disease process.

NK-1 antagonist reduces colonic inflammation and oxidative stress in dextran sulfate-induced colitis in rats

Although substance P (SP) has been implicated as a mediator of neurogenic inflammation in the small intestine, little information is available regarding the role of SP in the pathogenesis of chronic ulcerative colitis. In this study, our aim was to investigate whether the intraperitoneal administration of a nonpeptide neurokinin-1 (NK-1) antagonist, CP-96345, which antagonizes the binding of SP to its NK-1 receptor, results in the attenuation of colonic inflammation induced in rats by 5% dextran sodium sulfate (DSS) in drinking water for 10 days compared with an inactive enantiomer, CP-96344. Disease activity was assessed daily for 10 days, after which colonic tissue damage was scored and myeloperoxidase activity and colon and urinary 8-isoprostanes were measured. Animals receiving DSS exhibited marked physical signs of colitis by day 5 compared with controls. Chronic administration of the NK-1 antagonist significantly reduced the disease activity index, mucosal myeloperoxidase activity, colonic tissue damage score, and mucosal and urinary levels of 8-isoprostanes compared with inactive enantiomer- or vehicle-injected (saline) animals receiving DSS alone. These data indicate that the administration of an NK-1 antagonist can attenuate colonic inflammation and oxidative stress and suggest a novel therapeutic approach in the treatment of chronic ulcerative colitis.

Role of a hyaluronate-based membrane in the prevention of peritonitis-induced adhesions

Adhesions remain a significant postoperative complication of abdominal surgery; however, recent evidence suggests that physical barriers may reduce their incidence. Although these adhesion prevention barriers are efficacious when used under aseptic conditions, little is known about their use in the presence of peritonitis, which is associated with an increased incidence of abdominal adhesions. A sodium hyaluronate and carboxymethylcellulose bioresorbable membrane (HA membrane) has been shown recently to reduce postoperative adhesions in several animal models and in two clinical trials. To investigate the efficacy of HA membrane in the presence of peritonitis, generalized peritonitis was induced in rats by either cecal ligation and puncture (CLP) or cecal ligation (CL) alone. The ceca were resected after 12 hours, and animals were randomly assigned to receive or not receive HA membrane applied to the cecum. At day 7, abdominal adhesions and abscesses were scored. In the presence of peritonitis, HA membrane did not significantly reduce the number or tenacity of adhesions. A trend toward increased abscess formation was associated with HA membrane in the CL group. Although HA membrane has been shown to reduce the incidence and severity of abdominal adhesions under aseptic conditions, this study demonstrates that it is not efficacious in preventing abdominal adhesions in the presence of peritonitis. The association between HA membrane and abscess formation in the presence of experimental peritonitis requires further investigation.

Role of transforming growth factor beta-1 in peritonitis-induced adhesions

Peritonitis is a major cause of intra-abdominal adhesion formation. The overexpression of transforming growth factor beta-1 (TGF-Beta1), a potent mitogen, chemoattractant, and stimulant for collagen synthesis by fibroblasts, has been linked to tissue fibrosis at various sites throughout the body including peritoneal adhesion formation. Hence we hypothesized that the mechanism(s) involved in peritonitis-induced adhesion formation may be mediated through the upregulation of TGF-Beta1 expression. Peritonitis was induced in rats by cecal ligation and puncture, while a control group underwent sham operation. Adhesions were scored and harvested from both groups at 0, 6 and 12 hours and at 1, 2, 4, 7, and 28 days. Tissue expression of TGF-Beta1 mRNA was determined by quantitative reverse transcription-polymerase chain reaction and TGF-Beta1 protein was localized by immunohistochemical analysis. Serum and peritoneal fluid TGF-Beta1 concentrations were quantified by enzyme-linked immunosorbent assay. Compared with sham operation, peritonitis was associated with a significantly greater incidence of abdominal adhesions and a significant increase in the levels of TGF-Beta1 mRNA expression at days 2, 4, and 7. Immunostaining intensity of TGF-Beta1 in adhesions from the peritonitis group also steadily rose through day 7. In peritoneal fluid, the ratio of active:total TGF-Beta1 was significantly increased in the peritonitis group on days 1, 2, and 4 compared with the sham group. These results suggest that peritonitis is associated with the upregulation of TGF-Beta1, a mechanism that may exacerbate adhesion formation.

Role of stasis and oxidative stress in ileal pouch inflammation

BACKGROUND

Although ileal pouch-anal anastomosis has become the operation of choice for patients with chronic ulcerative colitis and familial adenomatous polyposis coli, ileal pouch inflammation or pouchitis remains a significant postoperative complication. Numerous factors such as fecal stasis have been implicated in the etiology of pouchitis; however, pouchitis remains poorly understood due to the lack of a small animal model. One of the primary goals of this study was to surgically create a reservoir or U-pouch in the ileum of a rat in which stasis would occur in a manner that was unimpeded by other complicating factors such as a colectomy. This model would allow investigation of the hypothesis that intestinal stasis leads to biochemical changes that predispose the ileal pouch to inflammation and oxidative stress.

MATERIALS AND METHODS

A U-pouch was surgically created in the terminal ileum of Lewis rats just proximal to the ileocecal valve without a colectomy. Stasis was assessed by serial barium radiographs over 48 h. Thirty days after surgery, mucosa was obtained from the ileal U-pouches and nonoperated ileum to assess inflammation and neutrophil infiltration histologically and by measuring myeloperoxidase activity. Oxidative stress was assessed by measuring 8-isoprostane levels in urine. Once the model was validated and it was established that stasis and inflammation occurred in the pouch, either vitamin E or allopurinol was administered for 30 days after which myeloperoxidase and 8-isoprostane levels were again measured.

RESULTS

In our experimental model, ileal stasis resulted in increases in both mucosal myeloperoxidase activity and urinary 8-isoprostane levels, suggesting that oxidative stress was associated with stasis. Thirty-day treatment with vitamin E or allopurinol reduced ileal myeloperoxidase activity and urinary 8-isoprostane levels.

CONCLUSION

These studies demonstrated that stasis in the ileum occurred and was associated with neutrophil infiltration and oxidative stress. Antioxidant treatment reduced the inflammatory response suggesting a role for antioxidant therapy in the treatment of pouchitis.

Ileal pouch salvage following failed ileal pouch- anal anastomosis

Attempts have been made to salvage failed ileal pouch-anal anastomoses (IPAA) performed for ulcerative colitis or familial polyposis coli. These can be categorized as total reconstruction of the IPAA, partial transabdominal approach, and partial transperineal approach. The aims of our study were to determine the overall success of pouch salvage; to examine the demographics, indications, and outcomes for each approach; and to assess anorectal physiology and patient satisfaction in those with successful salvage operations. We reviewed data, including results of anorectal manometry, from 29 patients undergoing salvage procedures for failed IPAA. Seventeen salvage attempts were successful, 11 attempts failed, and one patient was lost to follow-up. Success rates were 100% in the total reconstruction group, 25% in the partial transabdominal group, and 55% in the transperineal group. In those undergoing total reconstruction of the IPAA (n = 9), functional outcome, as measured by incontinence, improved with 50% reporting incontinence preoperatively compared to 0% postoperatively (P = 0.055). Mean 24-hour stool frequency and nighttime stool frequency declined. All patients reported satisfaction with their outcomes. Sixty percent of patients who underwent ileal pouch salvage following IPAA have been successful in avoiding permanent ileostomy. These results suggest that a continued effort to salvage failed IPAA, including the use of total reconstruction, is a viable alternative to permanent ileostomy.

Dietary cholesterol affects serum lipids, lipoproteins and LDL metabolism in cynomolgus monkeys in a dose-dependent manner

To examine the mechanism(s) underlying the cholesterolemic response to dietary cholesterol and saturated fatty acids, low density lipoprotein (LDL) metabolism was studied in two groups of cynomolgus monkeys fed diets containing 30 or 36% of total energy as fat. At each dietary fat level, the same group of monkeys was sequentially fed three dietary cholesterol concentrations as egg yolk in the following sequence: low (0.01 mg/kJ), medium (0.03 mg/kJ) and high (0.05 mg/kJ) for 30, 32 and 24 wk, respectively. Dietary polyunsaturated and monounsaturated fatty acids were the same in the two groups; the 6% difference in fat was due to the saturated fatty acids, 12:0 and 14:0. Serum total cholesterol, LDL cholesterol and LDL apolipoprotein B concentrations increased (P < 0.05) with dietary cholesterol in a dose-dependent manner in both fat groups. These elevations were the result of generally increasing LDL apolipoprotein B production rates, concomitant with reduced LDL apolipoprotein B fractional clearance at the high cholesterol intake. Serum HDL cholesterol and HDL apolipoprotein A-I concentrations were not affected in a consistent manner. These results demonstrate that cynomolgus monkeys are hyperresponsive to dietary cholesterol compared with humans, suggesting that this model may be useful in identifying metabolic and genetic predictors for hyperresponsiveness to dietary cholesterol in humans as well as assessing the metabolic heterogeneity of responses to dietary cholesterol.

LDL receptor activity is down-regulated similarly by a cholesterol-containing diet high in palmitic acid or high in lauric and myristic acids in cynomolgus monkeys

To determine the mechanisms whereby diets differing widely in fatty acid composition affect plasma LDL cholesterol and apolipoprotein B concentrations, LDL kinetics and receptor- and nonreceptor-mediated LDL catabolism were investigated in 27 cynomolgus monkeys fed diets containing 0.05 mg cholesterol/kJ and 40% fat energy as corn oil alone (unsaturated fat diet rich in oleic and linoleic acids), nonhydrogenated coconut oil alone (saturated fat diet, rich in lauric and myristic acids) or an oil blend (rich in palmitic acid). Consumption of the oil blend and saturated fat diets significantly elevated total cholesterol, LDL cholesterol and apolipoprotein B concentrations relative to the unsaturated fat diet and the saturated fat diet significantly increased plasma total cholesterol and LDL cholesterol compared with the oil blend diet. However, despite the greater increases in plasma total cholesterol, LDL cholesterol and apolipoprotein B in the saturated fat vs. the oil blend dietary group, the receptor-mediated LDL fractional catabolic rate was comparable in the oil blend and saturated fat diet groups. In addition, consumption of the oil blend or saturated fat diet increased the production rate of LDL apolipoprotein B and nonreceptor-mediated LDL apolipoprotein B transport (disposal) relative to the unsaturated fat diet. Our data, therefore, suggest that consumption of the oil blend or saturated fat diet elevated plasma total cholesterol and LDL cholesterol relative to the unsaturated fat diet, and the oil blend diet abundant in palmitic acid seems to have down-regulated the LDL receptor as much as a more saturated fat diet abundant in lauric and myristic acids.

Diets enriched in unsaturated fatty acids enhance apolipoprotein A-I catabolism but do not affect either its production or hepatic mRNA abundance in cynomolgus monkeys

To determine the mechanisms whereby dietary fatty acids influence high density lipoprotein (HDL) cholesterol and apolipoprotein (apo) A-I concentrations, ten cynomolgus monkeys were fed each of three experimental diets enriched in saturated (SAT), monounsaturated (MONO), or polyunsaturated (POLY) fatty acids in a crossover design consisting of three 13-week periods, with each animal serving as its own control. Each diet contained 30% of energy as fat with 0.22 mg cholesterol/kcal and differed solely by the isocaloric substitution of fatty acids as 18% of total energy calories. The replacement of dietary saturated fatty acids with either monounsaturated or polyunsaturated fatty acids, respectively, resulted in significant reductions of plasma total cholesterol (-17%; -30%), HDL cholesterol (-32%; -41%), and apo A-I (-37%; -44%) concentrations, while no significant differences were noted in plasma lipid or apo A-I concentrations when the MONO and POLY phases were compared. Although the MONO and POLY diets were similar in their effects on plasma lipids and apolipoproteins, the HDL of monkeys fed the POLY diet, as compared with either the SAT or the MONO diets, contained more cholesteryl ester and phospholipid but less total protein, resulting in a significantly lower total lipid to protein constituent ratio. Metabolic experiments revealed that the significantly lower plasma apo A-I concentrations observed during both the MONO and POLY phases relative to SAT were directly attributable to enhanced HDL apo A-I catabolism. Conversely, neither HDL apo A-I production rates nor hepatic apo A-I mRNA concentrations were significantly affected by dietary fatty acid perturbation in this study. Taken together, these data indicate that fractional catabolic rate is the predominant mechanism by which dietary fatty acids differentially modulate circulating concentrations of HDL apo A-I in this species when all other dietary variables are held constant.

Pharmacological properties of a novel ACAT inhibitor (CP-113,818) in cholesterol-fed rats, hamsters, rabbits, and monkeys

The novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor CP-113,818 has been characterized in vitro against ACAT isolated from liver and intestine from a variety of species including human subjects, and in vivo in cholesterol-fed rats, hamsters, rabbits, and two species of nonhuman primates. CP-113,818 is a potent and specific inhibitor of liver and intestinal ACAT with IC50s ranging from 17 to 75 nM. This ACAT inhibitor also prevented the absorption of exogenous radiolabeled cholesterol in hamsters (ED50 = 6 micrograms/kg), rabbits (ED50 1/2 10 micrograms/kg), and cynomolgus and African green monkeys (40 and 26% inhibition at 10 mg/kg, respectively). CP-113,818 effectively prevented the increase in liver cholesterol levels in cholesterol-fed rats, hamsters, and rabbits. In lipoprotein characterization studies in rabbits, CP-113,818 selectively decreased apoB-containing lipoproteins (beta-VLDL, IDL, and LDL) and shifted the distribution of cholesterol from beta-VLDL, IDL, and LDL (96% before treatment to 81% after treatment) to HDL (4% before treatment to 19% after treatment). Finally, in monkeys, CP-113,818 significantly decreased LDL cholesterol by approximately 30% while either increasing HDL cholesterol (cynomolgus monkeys) or not affecting HDL cholesterol (African green monkeys), thereby improving the total plasma cholesterol/HDL ratios. In summary, CP-113,818 significantly inhibited cholesterol absorption, prevented the increase in liver cholesterol, and improved the lipoprotein profiles by selectively decreasing the cholesterol concentrations of the atherogenic lipoproteins (VLDL, IDL, and LDL) in a variety of cholesterol-fed animals. These data suggest that ACAT inhibition may be a useful therapeutic approach for lowering LDL cholesterol and thereby reducing the risk of developing coronary heart disease.

Human plasma LDL cryopreserved with sucrose maintains in vivo kinetics indistinguishable from freshly isolated human LDL in cynomolgus monkeys

We previously reported that freeze-thawing of LDL causes marked alterations in its structure and in vitro biological behavior, and that such changes can be completely abolished by the addition of sucrose to the LDL solution prior to freezing. (Rumsey, S. C. et al., J. Lipid Res. 1992. 33: 1551-1561). We now questioned whether the cryopreservative action of sucrose would be equally effective in maintaining the in vivo metabolic characteristics of LDL. Two dual-label LDL turnover studies were performed in cynomolgus monkeys (n = 8) comparing freshly isolated human LDL with human LDL that was frozen in sucrose (10% w/v) for a short (20 h) or long period (6 months). The same sucrose-cryopreserved LDL was used for both the short- and long-term studies; different fresh LDL preparations were used in each study. Absorption spectrophotometry, gel filtration, and electron microscopy of LDL samples frozen with sucrose showed no evidence of physical alterations or aggregation, and there was no evidence of very rapid clearance of cryopreserved LDL from monkey plasma after injection. Fractional catabolic rates (FCR) of fresh and frozen LDL were very similar in either the short-term or long-term experiments: 2.09 +/- 0.86 versus 2.16 +/- 0.88, short-term and 3.03 +/- 2.28 versus 3.08 +/- 2.29, long-term (pools per day; mean +/- SD). The difference between FCR of fresh and frozen LDL for each animal averaged -0.076 +/- 0.074 and 0.01 +/- 0.22 (mean +/- SD), for short-term and long-term freezing, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of doxazosin on platelet aggregation, platelet adhesion and blood coagulation in cynomolgus monkeys

The effect of doxazosin, a selective alpha-1 adrenergic inhibitor, on hemostasis was investigated in 9 cynomolgus monkeys. During 12 weeks of doxazosin treatment (1 mg/kg per day), serum lipids, lipoprotein cholesterols, blood coagulation, platelet aggregation and template bleeding times were measured and compared with predrug values. In addition, platelet adhesion to cultured human umbilical vein endothelial cells (HUVEC) in the presence or absence of doxazosin was evaluated. Platelet aggregation was also determined in monkeys following chronic oral exposure to aspirin (162 mg/day). Doxazosin administration was associated with significant reductions in serum total cholesterol (TC) (-16%) and low density lipoprotein cholesterol (LDL-C) (-23%), while high density lipoprotein cholesterol (HDL-C) levels increased 66%. Doxazosin did not alter any parameters of blood coagulation measured; however, bleeding times were increased significantly (33%) in doxazosin-treated animals. Although collagen-stimulated platelet aggregation was not influenced by either chronic doxazosin or aspirin treatment, the maximal extent of ADP-stimulated platelet aggregation was significantly reduced (-26% and -18%, respectively) compared with the control monkeys. Platelets from untreated control animals displayed reductions in the extent of ADP-stimulated aggregation of 13% and 23%, respectively, when incubated in vitro with 200 and 300 micrograms/ml of doxazosin. Additionally, the decrease in aggregation response of platelets obtained from doxazosin-treated monkeys was accompanied by a rapid reversal of platelet aggregation. Adhesion to HUVEC by platelets isolated from doxazosin-treated animals was significantly decreased; however, adhesion was not altered when platelets from untreated control animals were incubated with HUVEC in the presence of doxazosin. Thus, the ex vivo and in vitro studies reported in this communication suggest that doxazosin administration to nonhuman primates is associated with beneficial alterations in plasma lipids, platelet aggregation, bleeding times and platelet adhesion to endothelial cells, parameters which are thought to influence risk of cardiovascular disease in both animals and humans.

A diet enriched in monounsaturated fats decreases low density lipoprotein concentrations in cynomolgus monkeys by a different mechanism than does a diet enriched in polyunsaturated fats

To determine the mechanisms whereby dietary fat saturation influences LDL cholesterol and apolipoprotein B concentrations, 10 cynomolgus monkeys were fed each of three experimental diets enriched in saturated, monounsaturated or polyunsaturated fatty acids in a crossover design consisting of three 13-wk periods. Each diet contained 30% of energy as fat with 0.05 mg cholesterol/kJ and differed solely by the isocaloric substitution of fatty acids as 60% of total fat energy. The replacement of dietary saturated fatty acids with either mono- or polyunsaturated fatty acids resulted in significant reductions of plasma total cholesterol (-17% and -30%, respectively), HDL cholesterol (-32% and -41%, respectively), apoA-1 (-37% and -44%, respectively), and apolipoprotein B (-28% and -36%, respectively) concentrations. Additionally, when dietary polyunsaturated fatty acids were substituted for saturated fatty acids, a 27% reduction in VLDL + LDL cholesterol was significant. Metabolic experiments suggested that the significantly reduced concentrations of apolipoprotein B observed during the monounsaturated and polyunsaturated fatty acid phases relative to the saturated fatty acid phase could not be entirely explained by changes in LDL apolipoprotein B clearance but rather were likely due to decreased LDL apolipoprotein B production rates. However, enhanced LDL apolipoprotein B catabolism accounted for the even greater reductions in VLDL + LDL cholesterol and apolipoprotein B concentrations observed during the polyunsaturated fatty acid phase vs. the monounsaturated fatty acid phase. Our data suggest that monounsaturated and polyunsaturated fatty acids lower apolipoprotein B concentrations by distinct mechanisms, with polyunsaturated fatty acids affecting LDL apolipoprotein B catabolism as well as production.

Unidirectional transfer in vivo of high-density lipoprotein cholesteryl esters to lower-density lipoproteins in the pig, an animal species without plasma cholesteryl ester transfer activity

The metabolism of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesteryl esters (CE) was studied in the pig, an animal species without plasma cholesteryl ester transfer activity (CETA). In the first series of experiments, LDL and HDL from normocholesterolemic pigs were radiolabeled with cholesteryl (1-14C)oleate and intravenously administered to two groups of four normocholesterolemic pigs. Radioactive tracer in LDL remained associated with the LDL fraction, and there was no transfer of LDL-CE to HDL. The transport rate (which represents the production and disposal rate) of LDL-CE in normocholesterolemic pigs was 39 mumol CE/h/L. However, radiolabeled HDL-CE were transferred to LDL (25%), and 36% of the LDL-CE mass was derived from the HDL. The transport rate of HDL-CE was 54 mumol CE/h/L, and the flux of HDL-CE to LDL was 14 mumol CE/h/L. There was no accumulation of radiolabeled HDL-CE in very-low-density lipoprotein (VLDL), which suggests that there was no transfer to VLDL. However, this does not rule out the possibility that either the very low levels of VLDL-CE (< 0.09 mmol/L) or the rapid turnover rate of the VLDL pool might have prevented the accumulation of substantial amounts of tracer in VLDL. Therefore, in a second set of experiments, the kinetics of HDL-CE were studied in high-fat-and high-cholesterol-fed pigs with elevated VLDL-CE concentrations (1.92 mmol/L). Hypercholesterolemia was associated with increased transport rates of LDL-CE (165 mumol/h/L) and HDL-CE (78 mumol/h/L) and with an increased flux of HDL-CE to LDL (78 mumol/h/L).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of doxazosin, an alpha 1-adrenergic inhibitor, on plasma lipid and lipoprotein levels, low density lipoprotein metabolism and cholesterol absorption in cynomolgus monkeys

The mechanism(s) by which doxazosin, an alpha 1 inhibitor, regulates plasma low density lipoprotein cholesterol (LDL-C) and apolipoprotein B (apo B) levels were investigated in 'normocholesterolemic' (average total cholesterol (TC) of 218 mg/dl) and 'hypercholesterolemic' (average TC of 350 mg/dl) cynomolgus monkeys. Twelve weeks of doxazosin treatment (1 mg/kg per day) significantly reduced plasma TC and LDL-C levels in both groups while high density lipoprotein cholesterol and apolipoprotein A-I concentrations rose. Despite these changes in plasma lipids, LDL and HDL lipid composition was not affected by doxazosin. The reduction in LDL-C and apo B in the doxazosin-treated 'hypercholesterolemic' group was associated with a significant increase in both receptor-dependent and -independent LDL apo B fractional catabolic rates. Similar associations were noted in the 'normocholesterolemic' group. LDL apo B production or transport rate was not affected by doxazosin. Cholesterol absorption was also significantly reduced by doxazosin which may also contribute to lowering plasma LDL-C levels. These studies suggest that doxazosin treatment can produce beneficial changes in the plasma lipid profile over a wide rage of plasma cholesterol levels by up-regulating LDL fractional clearance.

Dose-related effects of doxazosin on plasma lipids and aortic fatty streak formation in the hypercholesterolemic hamster model

Doxazosin, an alpha 1-adrenergic inhibitor, has been shown to decrease hypertension and plasma lipids, especially total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C), thus reducing certain risk factors associated with increased incidence of cardiovascular disease. One preliminary report indicated that the decrease in LDL-C in hypercholesterolemic hamsters treated with doxazosin was associated with a reduction in fatty streak formation. However, since the effects of doxazosin on plasma lipids, aortic fatty streak development, or the relationship between the two have not been studied in a dose-dependent manner, these effects were further investigated over varying doses of doxazosin (0, 1, 5, 10, and 20 mg/kg body wt/day) during a 10-week period. Doxazosin administration was associated with a dose-dependent decrease in LDL-C of 2%, 29%, 52%, and 60%, whereas the degree of fatty streak formation was reduced 11%, 45%, 76%, and 92% compared with controls, with the first statistically significant decrease for both parameters at the 10 mg/kg dose. Significant correlations between LDL-C concentrations and fatty streak area suggest that doxazosin altered aortic lipid infiltration primarily by its effect on plasma lipids. However, the 20 mg/kg dose of doxazosin significantly decreased lesion area compared with the 10 mg/kg dose without a further effect on plasma lipid concentrations. Three animals at these higher doses demonstrated no stainable lipid inclusions while maintaining plasma lipid values similar to their cohorts. These exceptions to the lipid-lesion relationship raise the possibility of additional effects of doxazosin, which may occur independent of or in concert with lipoprotein cholesterol lowering, on lesion formation.

Effects of dietary fats and cholesterol on liver lipid content and hepatic apolipoprotein A-I, B, and E and LDL receptor mRNA levels in cebus monkeys

The effects of the long-term administration of the dietary fats coconut oil and corn oil at 31% of calories with or without 0.1% (wt/wt) dietary cholesterol on plasma lipoproteins, apolipoproteins (apo), hepatic lipid content, and hepatic apoA-I, apoB, apoE, and low density lipoprotein (LDL) receptor mRNA abundance were examined in 27 cebus monkeys. Relative to the corn oil-fed animals, no significant differences were noted in any of the parameters of the corn oil plus cholesterol-fed group. In animals fed coconut oil without cholesterol, significantly higher (P less than 0.05) plasma total cholesterol (145%), very low density lipoprotein (VLDL) + LDL (201%) and high density lipoprotein (HDL) (123%) cholesterol, apoA-I (103%), apoB (61%), and liver cholesteryl ester (263%) and triglyceride (325%) levels were noted, with no significant differences in mRNA levels relative to the corn oil only group. In animals fed coconut oil plus cholesterol, all plasma parameters were significantly higher (P less than 0.05), as were hepatic triglyceride (563%) and liver apoA-I (123%) and apoB (87%) mRNA levels relative to the corn oil only group, while hepatic LDL receptor mRNA (-29%) levels were significantly lower (P less than 0.05). Correlation coefficient analyses performed on pooled data demonstrated that liver triglyceride content was positively associated (P less than 0.05) with liver apoA-I and apoB mRNA levels and negatively associated (P less than 0.01) with hepatic LDL receptor mRNA levels. Liver free and esterified cholesterol levels were positively correlated (P less than 0.05) with liver apoE mRNA levels and negatively correlated (P less than 0.025) with liver LDL receptor mRNA levels. Interestingly, while a significant correlation (P less than 0.01) was noted between hepatic apoA-I mRNA abundance and plasma apoA-I levels, no such relationship was observed between liver apoB mRNA and plasma apoB levels, suggesting that the hepatic mRNA of apoA-I, but not that of apoB, is a major determinant of the circulating levels of the respective apolipoprotein. Our data indicate that a diet high in saturated fat and cholesterol may increase the accumulation of triglyceride and cholesterol in the liver, each resulting in the suppression of hepatic LDL receptor mRNA levels. We hypothesize that such elevations in hepatic lipid content differentially alter hepatic apoprotein mRNA levels, with triglyceride increasing hepatic mRNA concentrations for apoA-I and B and cholesterol elevating hepatic apoE mRNA abundance.

Effect of corn and coconut oil-containing diets with and without cholesterol on high density lipoprotein apoprotein A-I metabolism and hepatic apoprotein A-I mRNA levels in cebus monkeys

The mechanism(s) by which diets containing corn or coconut oil (31% of energy as fat) totally free of cholesterol or with 0.1% added cholesterol by weight (0.3 mg/kcal) affect plasma high density lipoprotein cholesterol (HDL-C), apoprotein (apo) A-I levels, apo A-I kinetics, and hepatic apo A-I mRNA concentrations were investigated in 26 cebus monkeys. Coconut oil-fed monkeys had elevated levels of plasma total cholesterol (217%), very low density lipoprotein plus low density lipoprotein cholesterol (331%), HDL-C (159%), and apo A-I (117%) compared with corn oil-fed animals. Although the addition of cholesterol to the corn oil diet significantly increased these parameters, no such effects were seen when cholesterol was added to the coconut-oil diet. Both the type of fat and cholesterol in the diet significantly affected HDL apo A-I metabolism by decreasing apo A-I fractional catabolic rate and increasing apo A-I production rate in the coconut oil-fed groups. The decrease in apo A-I fractional catabolic rate in the coconut oil-fed animals was also associated with an increase in the HDL core lipid to surface ratio. Liver apo A-I mRNA abundance was elevated in the coconut oil-fed groups; however, dietary cholesterol had no affect on these levels. The lack of parallel effects of dietary fat and cholesterol on apo A-I production rate and liver apo A-I mRNA levels suggests that the increase in the apo A-I production rate observed in the coconut oil-fed groups resulted from the fat-induced rise in liver apo A-I mRNA abundance, whereas the cholesterol-induced rise in the apo A-I production rate resulted from a mechanism other than changes in liver apo A-I mRNA levels.

Estimation of HDL cholesteryl ester kinetic parameters in the cebus monkey, an animal species with high plasma cholesteryl ester transfer activity

We studied the kinetic parameters of high density lipoprotein (HDL) cholesteryl esters in the cebus monkey, an animal species with high plasma cholesteryl ester transfer activity. HDL were radiolabeled with cholesteryl [1-14C]oleate and intravenously administered to 4 cebus monkeys. The calculated fractional catabolic rate (FCR) of the HDL cholesteryl esters was 0.081 +/- 0.002 (mean +/- SD) h-1 and the calculated residence time was 12.3 +/- 0.3 h. The production or disposal rate of plasma HDL cholesteryl esters was 34.3 +/- 4.5 mumol/h. The radiolabeled cholesteryl esters were rapidly transferred from the HDL to the very low and low density lipoproteins (VLDL + LDL) and the amount of tracer in the VLDL + LDL had already reached a maximum at 3.5 +/- 0.7 h after tracer administration. The estimated fraction of VLDL + LDL cholesteryl esters derived from the HDL was 0.77 +/- 0.06. We also used radiolabeled [1,2-3H(N)]cholesteryl palmityl ether to trace HDL cholesteryl esters, but the ether tracer was more slowly cleared from the plasma and less readily transferred between plasma lipoproteins than the ester tracer.

The effect of exercise on plasma lipids and LDL subclass metabolism in miniature swine

The effects of exercise on plasma lipids and lipoproteins, high density lipoprotein (HDL) subclass cholesterol levels, and low density lipoprotein (LDL) subclass composition and metabolism were studied in Yucatan miniature swine following 2 yr of training. The exercise protocol produced significant training effects. Post-heparin lipolytic activity was also significantly increased. Although plasma cholesterol and triglycerides did not differ significantly (P = 0.08) between the exercised and control groups, multivariate analysis indicated a strong association between lipoprotein lipase (LPL) and HDL2-C (P less than 0.0001). Although HDL-C levels rose only slightly (P less than 0.09) with exercise, a significant shift was noted in the distribution of cholesterol from the HDL3 to the HDL2 fractions, perhaps mediated by the substantial increase in LPL activity. Exercise had little effect on the chemical composition of the major lipoprotein classes; however, the triglyceride content of the lighter LDL1 subclass was significantly reduced. In the more dense LDL2 subclass, exercise resulted in a significant decrease in triglycerides concomitant with a significant increase in free cholesterol levels. In contrast with the small reductions in fractional catabolic rates (FCR) in either subclass, production rates of the exercised group were reduced, which accounted for the reduction in LDL subclass pool size. These data indicate that exercise produces subtle but significant changes in lipoprotein metabolism that have been previously associated with reduced risk of atherosclerosis.

Comparative molecular properties of swine and human very low density lipoproteins-apoproteins E and C

1. By means of 2-dimensional gradient-gel electrophoresis, the very low density lipoproteins (VLDL) apoproteins E and C profiles from human and swine plasma were studied. 2. The molecular properties (isoelectric point and molecular weight) of the VLDL apoproteins and their isoforms were determined and showed many similarities between species. 3. It also appears evident that a previously unrecognized apoprotein (C-III) and several associated isoforms may exist in swine; however, it's mobility on 2-dimensional gradient gels is very similar to Apo C-II.

Effect of dietary fat saturation and cholesterol on LDL composition and metabolism. In vivo studies of receptor and nonreceptor-mediated catabolism of LDL in cebus monkeys

The mechanism(s) by which polyunsaturated fats reduce low density lipoprotein (LDL) cholesterol and apolipoprotein (apo) B were investigated in 20 cebus monkeys (Cebus albifrons) fed diets containing corn oil or coconut oil as fat (31% of calories) with or without dietary cholesterol (0.1% by weight) for 3 to 10 years. Coconut-oil feeding compared to corn-oil feeding resulted in significant increases in levels of plasma total cholesterol (176%), very low density lipoprotein (VLDL)-LDL cholesterol (236%), high density lipoprotein (HDL) cholesterol (148%), apo B (78%), and apo A-I (112%). The addition of dietary cholesterol to corn oil compared to corn oil alone resulted in smaller, but significant, increases in levels of total cholesterol (44%), HDL cholesterol (40%), and apo A-I (33%). Although the increases in VLDL-LDL cholesterol were of similar magnitude (52%), they barely failed to reach statistical significance (p less than 0.08), while the changes in apo B levels were negligible. The addition of dietary cholesterol to coconut oil, compared to coconut oil alone, resulted in no significant changes in lipoprotein cholesterol or apoproteins, although levels of VLDL-LDL cholesterol and apo B values increased 22% and 16%, respectively. Although hepatic free cholesterol content was not altered by diet, coconut-oil compared to corn-oil feeding resulted in significant increases in hepatic cholesteryl esters (236%) and triglycerides (325%), the latter increasing still further when dietary cholesterol was added to coconut oil (563%). To further assess the effects of these dietary changes on LDL metabolism, radioiodinated normal and glucosylated LDL kinetics were performed. The production rate of LDL apo B was not altered by diet. With corn-oil feeding, 63% of LDL catabolism was via the receptor-mediated pathway. Coconut-oil compared to corn-oil feeding resulted in a 50% decrease in receptor-mediated LDL apo B fractional catabolic rate (FCR) and a 27% reduction in nonreceptor-mediated LDL apo B FCR. The addition of dietary cholesterol to corn oil, compared to corn oil alone, resulted in no significant effect on LDL apo B catabolism. The addition of dietary cholesterol to coconut oil, compared to coconut oil alone, was associated with no significant change in nonreceptor catabolism of LDL apo B but with a 58% decrease in receptor-mediated catabolism of LDL (p less than 0.059). The diet-induced alterations of LDL catabolism were significantly correlated with hepatic lipids, which were enriched in saturated fatty acids.(ABSTRACT TRUNCATED AT 400 WORDS)