Bile diversion in rats leads to a decreased plasma concentration of linoleic acid which is not due to decreased net intestinal absorption of dietary linoleic acid

Modulation of Bile Acid Metabolism to Improve Plasma Lipid and Lipoprotein Profiles

New drugs targeting bile acid metabolism are currently being evaluated in clinical studies for their potential to treat cholestatic liver diseases, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Changes in bile acid metabolism, however, translate into an alteration of plasma cholesterol and triglyceride concentrations, which may also affect cardiovascular outcomes in such patients. This review attempts to gain insight into this matter and improve our understanding of the interactions between bile acid and lipid metabolism. Bile acid sequestrants (BAS), which bind bile acids in the intestine and promote their faecal excretion, have long been used in the clinic to reduce LDL cholesterol and, thereby, atherosclerotic cardiovascular disease (ASCVD) risk. However, BAS modestly but consistently increase plasma triglycerides, which is considered a causal risk factor for ASCVD. Like BAS, inhibitors of the apical sodium-dependent bile acid transporter (ASBTi’s) reduce intestinal bile acid absorption. ASBTi’s show effects that are quite similar to those obtained with BAS, which is anticipated when considering that accelerated faecal loss of bile acids is compensated by an increased hepatic synthesis of bile acids from cholesterol. Oppositely, treatment with farnesoid X receptor agonists, resulting in inhibition of bile acid synthesis, appears to be associated with increased LDL cholesterol. In conclusion, the increasing efforts to employ drugs that intervene in bile acid metabolism and signalling pathways for the treatment of metabolic diseases such as NAFLD warrants reinforcing interactions between the bile acid and lipid and lipoprotein research fields. This review may be considered as the first step in this process.

Cross-talk between liver and intestine in control of cholesterol and energy homeostasis

A major hurdle for organisms to dispose of cholesterol is the inability to degrade the sterol nucleus which constitutes the central part of the molecule. Synthesis of the sterol nucleus requires a complex, energy costly, metabolic pathway but also generates a diverse array of intermediates serving crucial roles in cellular energy metabolism and signal transduction. This may be the reason why this complex pathway has survived evolutionary pressure. The only way to get rid of substantial amounts of cholesterol is conversion into bile acid or direct excretion of the sterol in the feces. The lack of versatility in disposal mechanisms causes a lack of flexibility to regulate cholesterol homeostasis which may underlie the considerable human pathology linked to cholesterol removal from the body. Export of cholesterol from the body requires an intricate communication between intestine and the liver. The last decade this inter-organ cross talk has been focus of intense research leading to considerable new insight. This novel information on particular the cross-talk between liver and intestine and role of bile acids as signal transducing molecules forms the focus of this review.

Reduced absorption of long-chain fatty acids during methotrexate-induced gastrointestinal mucositis in the rat

BACKGROUND & AIMS

Patients with chemotherapy-induced gastrointestinal mucositis suffer from weight loss and possibly malabsorption. Since long-chain fatty acids serve important functions in the body, we aimed to determine the intestinal capacity of fat absorption in rats with and without methotrexate-induced mucositis.

METHODS

Four days after intravenous injection with methotrexate (60 mg/kg) or saline, rats received saturated ([U-(13)C]palmitic acid) and unsaturated ([U-(13)C]linoleic acid) fatty acids dissolved in oil, either as a single bolus by oral gavage or by continuous intraduodenal infusion. We determined plasma and liver label concentrations at specific time points.

RESULTS

We confirmed methotrexate-induced mucositis by villus atrophy using microscopy. Methotrexate treatment severely reduced the appearance of [U-(13)C]palmitic- and [U-(13)C]linoleic acid in plasma and liver, compared to controls, either when administered as a bolus or continuously (all at least -63%, P < 0.05). Liver [U-(13)C]palmitic acid appearance was higher than [U-(13)C]linoleic acid appearance, either when administered as a bolus (2.8-fold, P < 0.01) or continuously (5.7-fold, P < 0.01).

CONCLUSIONS

The intestinal capacity to absorb long-chain fatty acids is severely reduced in rats with methotrexate-induced mucositis. Continuous administration does not overcome this impairment. The liver takes up and/or retains mainly saturated fatty acids during mucositis.

Persistent fat malabsorption in cystic fibrosis; lessons from patients and mice

Fat malabsorption in pancreatic insufficient cystic fibrosis (CF) patients is classically treated with pancreatic enzyme replacement therapy (PERT). Despite PERT, intestinal fat absorption remains insufficient in most CF patients. Several factors have been suggested to contribute to the persistent fat malabsorption in CF (CFPFM). We reviewed the current insights concerning the proposed causes of CFPFM and the corresponding intervention studies. Most data are obtained from studies in CF patients and CF mice. Based on the reviewed literature, we conclude that alterations in intestinal pH and intestinal mucosal abnormalities are most likely to contribute to CFPFM. The presently available data indicate that acid suppressive drugs and broad spectrum antibiotics could be helpful in individual CF patients for optimizing fat absorption and/or nutritional status.

Production of conjugated linoleic acid and conjugated linolenic acid isomers by Bifidobacterium species

Conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) isomers have attracted great interest because of their potential health benefits. Formation of CLA and CLNA takes place in the rumen during biohydrogenation. Several studies have indicated that certain types of intestinal bacteria, including bifidobacteria, are able to convert linoleic acid (LA) to CLA. The role of intestinal bacteria in the formation of CLNA isomers is largely unknown. In the present study, a screening of 36 different Bifidobacterium strains for their ability to produce CLA and CLNA from free LA and alpha-linolenic acid (LNA), respectively, was performed. The strains were grown in MRS broth, to which LA or LNA (0.5 mg ml(-1)) were added after 7 h of bacterial growth. Cultures were further incubated at 37 degrees C for 72 h. Six strains (four Bifidobacterium breve strains, a Bifidobacterium bifidum strain and a Bifidobacterium pseudolongum strain) were able to produce different CLA and CLNA isomers. Conversion percentages varied from 19.5% to 53.5% for CLA production and from 55.6% to 78.4% for CLNA production among these strains. The CLA isomers produced were further identified with Ag(+)-HPLC. LA was mainly converted to t9t11-CLA and c9t11-CLA. The main CLNA isomers were identified with GC-MS as c9t11c15-CLNA and t9t11c15-CLNA.

Intestinal capacity to digest and absorb carbohydrates is maintained in a rat model of cholestasis

Cholestasis is associated with systemic accumulation of bile salts and with deficiency of bile in the intestinal lumen. During the past years bile salts have been identified as signaling molecules that regulate lipid, glucose, and energy metabolism. Bile salts have also been shown to activate signaling routes leading to proliferation, apoptosis, or differentiation. It is unclear, however, whether cholestasis affects the constitution and absorptive capacity of the intestinal epithelium in vivo. We studied small intestinal morphology, proliferation, apoptosis, expression of intestine-specific genes, and carbohydrate absorption in cholestatic (1 wk bile duct ligation), bile-deficient (1 wk bile diversion), and control (sham) rats. Absorptive capacity was assessed by determination of plasma [(2)H]- and [(13)C]glucose concentrations after intraduodenal administration of [(2)H]glucose and naturally enriched [(13)C]sucrose, respectively. Small intestinal morphology, proliferation, apoptosis, and gene expression of intestinal transcription factors (mRNA levels of Cdx-2, Gata-4, and Hnf-1alpha, and Cdx-2 protein levels) were similar in cholestatic, bile-deficient, and control rats. The (unlabeled) blood glucose response after intraduodenal administration was delayed in cholestatic animals, but the absorption over 180 min was quantitatively similar between the groups. Plasma concentrations of [(2)H]glucose and [(13)C]glucose peaked to similar extents in all groups within 7.5 and 30 min, respectively. Absorption of [(2)H]glucose and [(13)C]glucose in plasma was similar in all groups. The present data indicate that neither accumulation of bile salts in the body, nor their intestinal deficiency, two characteristic features of cholestasis, affect rat small intestinal proliferation, differentiation, apoptosis, or its capacity to digest and absorb carbohydrates.

Mechanisms of lipid malabsorption in Cystic Fibrosis: the impact of essential fatty acids deficiency

Transport mechanisms, whereby alimentary lipids are digested and packaged into small emulsion particles that enter intestinal cells to be translocated to the plasma in the form of chylomicrons, are impaired in cystic fibrosis. The purpose of this paper is to focus on defects that are related to intraluminal and intracellular events in this life-limiting genetic disorder. Specific evidence is presented to highlight the relationship between fat malabsorption and essential fatty acid deficiency commonly found in patients with cystic fibrosis that are often related to the genotype. Given the interdependency of pulmonary disease, pancreatic insufficiency and nutritional status, greater attention should be paid to the optimal correction of fat malabsorption and essential fatty acid deficiency in order to improve the quality of life and extend the life span of patients with cystic fibrosis.

Treatment of EFA deficiency with dietary triglycerides or phospholipids in a murine model of extrahepatic cholestasis

Essential fatty acid (EFA) deficiency during cholestasis is mainly due to malabsorption of dietary EFA (23). Theoretically, dietary phospholipids (PL) may have a higher bioavailability than dietary triglycerides (TG) during cholestasis. We developed murine models for EFA deficiency (EFAD) with and without extrahepatic cholestasis and compared the efficacy of oral supplementation of EFA as PL or as TG. EFAD was induced in mice by feeding a high-fat EFAD diet. After 3 wk on this diet, bile duct ligation was performed in a subgroup of mice to establish extrahepatic cholestasis. Cholestatic and noncholestatic EFAD mice continued on the EFAD diet (controls) or were supplemented for 3 wk with EFA-rich TG or EFA-rich PL. Fatty acid composition was determined in plasma, erythrocytes, liver, and brain. After 4 wk of EFAD diet, induction of EFAD was confirmed by a sixfold increased triene-to-tetraene ratio (T/T ratio) in erythrocytes of noncholestatic and cholestatic mice (P < 0.001). EFA-rich TG and EFA-rich PL were equally effective in preventing further increase of the erythrocyte T/T ratio, which was observed in cholestatic and noncholestatic nonsupplemented mice (12- and 16-fold the initial value, respectively). In cholestatic mice, EFA-rich PL was superior to EFA-rich TG in decreasing T/T ratios of liver TG and PL (each P < 0.05) and in increasing brain PL concentrations of the long-chain polyunsaturated fatty acids (LCPUFA) docosahexaenoic acid and arachidonic acid (each P < 0.05). We conclude that oral EFA supplementation in the form of PL is more effective than in the form of TG in increasing LCPUFA concentrations in liver and brain of cholestatic EFAD mice.

Abnormal regulation of serum lipid fatty acid profiles in short gut rats fed parenteral nutrition with lipid

Despite absence of essential fatty acid deficiency (EFAD), increases in arachidonic acid to linoleic acid ratios occur in serum phospholipid of patients treated with chronic total parenteral nutrition (TPN). The parenteral lipid component of TPN contains abundant linoleate; thus low phospholipid linoleate may reflect increased conversion to arachidonate. Arachidonic acid excess has been associated with a proinflammatory milieu through increased eicosanoid production and might contribute to the increases in inflammatory markers seen in home TPN patients. We investigated fatty acid metabolism in a rodent model of malabsorption. We hypothesized that short gut rats would metabolize parenteral lipid differently from intact rats. We performed laparotomy and 80% small bowel resection (or sham surgery) in rats. Sixteen sham and 16 short gut rats were randomly assigned to TPN with lipid or fat-free TPN. After 5 days, weight loss was similar in all groups. Analysis of serum phospholipids demonstrated that 20:3omega9 (eicosatrienoic acid) was relatively increased in fat-free TPN groups, irrespective of surgery type, as were distal very long chain omega3 class fatty acids, as anticipated. Uniquely, both nutrition (TPN/lipid v fat-free TPN) and surgery type (sham v short gut) were significant in determining arachidonic acid levels. Relatively elevated arachidonate occurred in both groups of fat-free rats, suggesting increased Delta6 and/or Delta5 desaturase activity, as expected. In contrast, giving TPN/lipid lowered arachidonate (suggesting appropriately downregulated desaturases) in sham animals, but not in short gut animals. Ratios of arachidonic and di-homo-gamma-linolenic to linoleic acids further suggested increased turnover of precursor omega6 to arachidonic acid in short gut rats given lipid compared with the other groups. These preliminary data show that intravenous (IV) lipid gave rise to serum lipid fatty acid profiles that differed in short gut and sham rats. The short gut rat may have a heightened hepatic desaturase activity, inappropriate for the quantity of linoleic acid provided parenterally. Therefore, the short gut rat is an appropriate model to study further arachidonic acid excess in home TPN patients.

Administration of phosphatidylcholine–cholesterol liposomes partially reconstitutes fat absorption in chronically bile-diverted rats

BACKGROUND AND AIMS

Intestinal bile deficiency in cholestatic patients leads to fat malabsorption. We addressed the potency of model bile, bile salts and phosphatidylcholine (PC)-cholesterol (CH) liposomes to reconstitute fat absorption in permanently bile-diverted (BD) rats.

METHODS

The plasma appearance of 13C-labeled palmitic acid (13C-16:0) and linoleic acid (13C-18:2) was determined after their enteral administration to BD or to control rats with an intact enterohepatic circulation (EHC) (13C-16:0 and 13C-18:2 dissolved in 25% olive oil-75% medium chain triacylglycerol oil mixture). BD rats were intraduodenally infused with buffer, model bile [consisting of 60 mM taurocholate (TC), 8 mM PC and 1 mM CH], buffer with TC, buffer with PC and CH liposomes, or buffer with lyso-PC and CH.

RESULTS

Plasma concentrations of 13C-16:0 and 13C-18:2 were consistently three- to eightfold higher in control rats than those in buffer-infused BD rats (P < 0.01). ID administration of either model bile or TC to BD rats restored plasma appearance of 13C-fatty acids at least to concentrations observed in control rats. Administration of PC + CH liposomes to BD rats partially reconstituted the plasma appearance of 13C-16:0, but did not affect that of 13C-18:2. Compared with control rats, the area under the curve (AUC) of plasma 13C-16:0 concentrations was 13.0 +/- 6.9% in buffer-infused rats and 40.9 +/- 3.1% in liposome-infused rats (P < 0.005).

CONCLUSIONS

Enteral administration of PC + CH liposomes to BD rats partially corrects the absorption of palmitic acid. Present data suggest that administration of PC + CH liposomes could enhance fat absorption in clinical conditions of cholestasis in which bile salt supplemention is contraindicated.

Orlistat treatment increases fecal bilirubin excretion and decreases plasma bilirubin concentrations in hyperbilirubinemic Gunn rats

OBJECTIVE

To determine whether serum levels of unconjugated bilirubin (UCB) can be decreased by enhancing fecal fat excretion.

STUDY DESIGN

Gunn rats were fed a high-fat diet (control) or the same diet mixed with the lipase inhibitor orlistat. At regular intervals, plasma UCB concentrations were determined and 72-hour fat balances were performed.

RESULTS

Orlistat treatment decreased plasma UCB concentrations (at 3 weeks; 100 mg/kg, -33%+/-8%, P<.05; 200 mg/kg, -46%+/-10%, P<.01). Within days of treatment, orlistat treatment increased fecal excretion of UCB (at day 3; +220%, P<.05). During 24 weeks of orlistat treatment (200 mg/kg diet), the plasma bilirubin concentrations were continuously approximately 35% lower than in control rats. Plasma UCB concentrations were inversely correlated with the amount of fecal fat excretion (n=12, r=-0.87, P<.001).

CONCLUSIONS

In Gunn rats, orlistat treatment increases the fecal excretion of fat and enhances the disposal of UCB. This approach could lead to novel strategies for prevention and treatment of unconjugated hyperbilirubinemia in patients.

Functional development of fat absorption in term and preterm neonates strongly correlates with ability to absorb long-chain Fatty acids from intestinal lumen

Our goal for this study was to determine whether the maturation of fat absorption in neonatal life is functionally related to an increased ability to hydrolyze dietary fat, to absorb long-chain fatty acids, or to do both. In 16 preterm and in eight term neonates, the intestinal ability to hydrolyze triacylglycerols and the capacity to absorb long-chain fatty acids were determined at several times between birth and 5 mo after the term age. These processes were compared with the percentage of fat absorption (formula-fed infants) or with fecal fat excretion (breast-fed infants). The functional capacity to digest triacylglycerols and to absorb the lipolytic products was evaluated by measuring serum concentrations of the lipolytic product [1-(13)C]palmitate after the enteral administration of tri-1-(13)C palmitoyl-glycerol. Long-chain fatty acids absorption (i.e. independent of lipolysis) was determined by measuring serum concentrations of [1-(13)C]stearate after its enteral administration. The efficacy of fat absorption increased in preterm infants (formula-fed) from 91.2 +/- 1.1% (mean +/- SEM) at 32.3 wk postconceptional age (PCA) to 97.3 +/- 0.6% at 53.6 wk PCA (p < 0.001), and in term infants from 91.7 +/- 1.8% (40.0 wk PCA) to 97.4 +/- 1.3% (58.9 wk PCA, p = 0.07). Both the serum concentration of [1-(13)C]stearate and that of [1-(13)C]palmitate appeared highly correlated with the efficacy of fat absorption (r = 0.82, p = 0.02; and r = 0.91, p = 0.004; respectively) and with PCA (r = 0.99, p < 0.001; and r = 0.85, p < 0.02; respectively). These results indicate that the functional development of fat absorption in preterm and term infants is related to the capacity to absorb long-chain fatty acids from the intestine.

Protection from obesity and insulin resistance in mice overexpressing human apolipoprotein C1

Apolipoprotein (APO) C1 is a 6.6-kDa protein present in plasma and associated with lipoproteins. Using hyperinsulinemic-euglycemic clamp tests, we previously found that in APOC1 transgenic mice, the whole-body insulin-mediated glucose uptake is increased concomitant with a decreased fatty acid uptake. These latter results are confirmed in the present study, showing that APOC1 transgenic mice exhibit a 50% reduction in the uptake of the fatty acid analog 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid in white adipose tissue stores. We next investigated whether APOC1 overexpression can modulate the initiation and/or development of obesity and insulin resistance. When crossbred on the genetically obese ob/ob background, APOC1 transgenic mice were fully protected from the development of obesity compared with ob/ob only mice, as reflected by a strong reduction in body weight (21 +/- 4 vs. 44 +/- 7 g), total adipose tissue stores (15 +/- 3 vs. 25 +/- 3% body wt), and average adipocyte size (7,689 +/- 624 vs. 15,295 +/- 1,289 microm(2)). Although less pronounced, APOC1 overexpression also reduced body weight on a wild-type background, solely due to a reduction in adipose tissue. Furthermore, despite elevated plasma free fatty acid and triglyceride levels, APOC1 overexpression significantly improved insulin sensitivity in ob/ob mice, as demonstrated by a strong reduction in plasma glucose and insulin levels, as well as a better performance in the glucose tolerance test. In conclusion, a marked reduction in the uptake of fatty acids into adipocytes may underlie the protection from obesity and insulin resistance in transgenic mice overexpressing human APOC1.

Nutritional effects of surgical and medical treatment for short bowel syndrome

BACKGROUND

The choice of treatment options in short bowel syndrome (SBS) is hampered by a lack of comparative studies. This study uses a previously validated juvenile pig model of SBS to compare nontreated controls (C), surgical treatment with either proximal colon interposition (CI) or bowel lengthening (BL), with medical treatment with codeine and cimetidine (M).

METHODS

Treatment was initiated 6 weeks after resection of 75% of the small bowel, and animals were followed until sacrifice at week 16. Feed intake and weight gain were monitored throughout; in vivo nutrient absorption, in vitro nutrient transport, sodium-glucose cotransporter activity, and intestinal morphology (gross and microscopic) were examined at the end of treatment.

RESULTS

BL and M treatments resulted in improved rates of weight gain; this improvement was associated with improved absorption of dietary fat. The treatments did not affect carbohydrate or protein absorption in vivo. In vitro fatty acid absorption was not increased in any group. Active uptake of glucose was increased in the colon interposition group, but phlorizin binding (reflecting sodium glucose cotransporter activity) did not differ between groups. Gross serosal and microscopic mucosal surface areas increased in all groups; however, there were no significant differences between the treatment groups.

CONCLUSIONS

These results demonstrate that bowel lengthening and medical treatment improved the rate of weight gain in this model of SBS. This appeared to be due to improvement in the absorption of dietary fat, which was not caused by alterations in in vitro uptake or mucosal surface area, suggesting these treatments have their affects by altering motility or intraluminal digestion. These findings suggest that these treatments are worthy of further study in treating patients (primary pediatric) with SBS.

Postprandial chylomicron clearance rate in late teenagers with diabetes mellitus type 1

A delayed chylomicron (CM) clearance rate, a known risk factor for atherosclerosis, has been described in adults with diabetes type 1 (DM1). We determined the CM clearance rate in late teenagers with DM1, and the relationship between CM clearance rate and elevated plasma lipid concentrations in DM1 teenagers in poor metabolic control (as characterized by HbA(1c) percentage). Plasma lipids and CM clearance were determined in nine patients with DM1 (mean age +/- SD: 17.5 +/- 0.6 y) and four healthy controls (mean age +/- SD: 20.1 +/- 0.8 y), by measuring breath (13)CO(2), plasma triglyceride, retinyl palmitate, and (13)C-labeled oleic acid concentrations, after oral administration of a fat-rich meal together with vitamin A and (13)C-oleic acid. In patients with DM1, fasting triglyceride and cholesterol concentrations were positively correlated with HbA(1c) percentage (p < 0.05). Neither in DM1 patients, nor in controls, was an elevated triglyceride concentration (above 1.7 mmol/L) found. Yet, in 22% of DM1 patients, cholesterol concentration was above 5.2 mmol/L, but not in any of the controls. CM clearance rate in DM1 patients was similar to that in controls and did not significantly correlate with HbA(1c) percentage. Fasting lipid concentrations in DM1 patients were not significantly correlated with CM clearance rate. Present data indicate that elevated lipid concentrations in late teenagers with DM1 are not attributable to a delay in CM clearance rate. A delayed CM clearance rate at late teenager age is not a risk factor contributing to the increased risk for atherosclerosis in DM1.

Down-regulation of intestinal scavenger receptor class B, type I (SR-BI) expression in rodents under conditions of deficient bile delivery to the intestine

Scavenger receptor class B, type I (SR-BI) is expressed in the intestines of rodents and has been suggested to be involved in the absorption of dietary cholesterol. The aim of this study was to determine whether intestinal SR-BI expression is affected in animal models with altered bile delivery to the intestine and impaired cholesterol absorption. SR-BI protein and mRNA levels were determined in proximal and distal small intestine from control, bile-duct-ligated and bile-diverted rats and from control and bile-duct-ligated mice. Two genetically altered mouse models were studied: multidrug resistance-2 P-glycoprotein-deficient [Mdr2((-/-))] mice that produce phospholipid/cholesterol-free bile, and cholesterol 7alpha-hydroxylase-deficient [Cyp7a((-/-))] mice, which exhibit qualitative and quantitative changes in the bile-salt pool. Cholesterol-absorption efficiency was quantified using a dual-isotope ratio method. SR-BI was present at the apical membrane of enterocytes in control rats and mice and was more abundant in proximal than in distal segments of the intestine. In bile-duct-ligated animals, levels of SR-BI protein were virtually absent and mRNA levels were decreased by approximately 50%. Bile-diverted rats, Mdr2((-/-)) mice and Cyp7a((-/-)) mice showed decreased levels of intestinal SR-BI protein while mRNA levels were unaffected. Cholesterol absorption was reduced by >90% in bile-duct-ligated and bile-diverted animals and in Cyp7a((-/-)) mice, whereas Mdr2((-/-)) mice showed an approximately 50% reduction. This study shows that SR-BI is expressed at the apical membrane of enterocytes of rats and mice, mainly in the upper intestine where cholesterol absorption is greatest, and indicates that bile components play a role in post-transcriptional regulation of SR-BI expression. Factors associated with cholestasis appear to be involved in transcriptional control of intestinal SR-BI expression. The role of SR-BI in the cholesterol-absorption process remains to be defined.

Intestinal absorption and postabsorptive metabolism of linoleic acid in rats with short-term bile duct ligation

We investigated in bile duct-ligated (BDL) and sham-operated control rats whether the frequent presence of essential fatty acid deficiency in cholestatic liver disease could be related to linoleic acid malabsorption, altered linoleic acid metabolism, or both. In plasma of BDL rats, the triene-to-tetraene ratio, a biochemical marker for essential fatty acid deficiency, was increased compared with controls (0.024 +/- 0.004 vs. 0.013 +/- 0.001; P < 0.05). Net and percentage of dietary linoleic acid absorbed were decreased in BDL rats compared with control rats (1.50 +/- 0.16 mmol/day and 81.3 +/- 3.3% vs. 2.08 +/- 0.07 mmol/day and 99.2 +/- 0.1%, respectively; each P < 0.001). At 24 h after [(13)C]linoleic acid administration, BDL rats had a similar ratio of plasma [(13)C]arachidonic acid to plasma [(13)C]linoleic acid concentration compared with control rats. Delta(6)-Desaturase activity was not significantly different in hepatic microsomes from control or BDL rats. At 3 h after [(13)C]linoleic acid administration, plasma appearance of [(13)C]linoleic acid and cumulative expiration of (13)CO(2) were decreased in BDL rats, compared with controls (by 54% and 80%, respectively). The present data indicate that the impaired linoleic acid status in cholestatic liver disease is mainly due to decreased net absorption and not to quantitative alterations in postabsorptive metabolism.

Detection of impaired intestinal absorption of long-chain fatty acids: validation studies of a novel test in a rat model of fat malabsorption

BACKGROUND

Classic fat balance studies detect fat malabsorption but do not discriminate between the potential causes of malabsorption, such as impaired intestinal lipolysis or reduced uptake of fatty acids.

OBJECTIVE

We aimed to validate a novel test for the specific, sensitive detection of impaired intestinal uptake of long-chain unesterified fatty acids in an appropriate rat model of fat malabsorption.

DESIGN

The absorption and appearance in plasma of [(13)C]palmitic acid were determined in control rats and in rats with fat malabsorption due either to chronic bile deficiency (permanent bile diversion) or to oral administration of the lipase inhibitor orlistat (200 mg/kg diet). [(13)C]Palmitic acid results were compared with the percentage absorption of ingested dietary fat determined by fat balance.

RESULTS

Between 1 and 6 h after intraduodenal administration, plasma [(13)C]palmitate concentrations in control rats were 4-10-fold higher than in bile-deficient rats (P < 0.05) but were not significantly different between orlistat-supplemented rats and their controls. In control and bile-deficient rats, plasma [(13)C]palmitate concentrations allowed complete discrimination between normal (>92%) and reduced (<92%) fat absorption, whereas the percentage absorption of [(13)C]palmitate over 48 h appeared to be highly correlated with the percentage absorption of ingested dietary fat (r = 0.89, P < 0.001).

CONCLUSIONS

The [(13)C]palmitic acid absorption test detects impaired intestinal absorption of long-chain fatty acids selectively and sensitively in a rat model of fat malabsorption due to bile deficiency. Our data strongly support the use of the [(13)C]palmitic acid absorption test for the diagnosis of clinical fat malabsorption syndromes.

Validation in an animal model of the carbon 13-labeled mixed triglyceride breath test for the detection of intestinal fat malabsorption

OBJECTIVE

To determine, in a rat model of fat malabsorption, the potency of the carbon 13-labeled mixed triglyceride ((13)C-MTG) breath test as a noninvasive, patient-friendly replacement for classic fat balance studies.

STUDY DESIGN

Comparison of the percentage of fat absorption, detected by fat balance, with the (13)CO(2) recovery of the (13)C-MTG breath test in rats fed high-fat chow and varying amounts of the lipase inhibitor, orlistat (0, 50, 200, and 800 mg per kilogram of chow), for 5 days.

RESULTS

On orlistat administration, total fat absorption decreased from 80.2% +/- 2.2% to 32.8% +/- 3.7% (mean +/- SEM, 0 mg and 800 mg of orlistat per kilogram of chow, respectively; P <.001). Correspondingly, breath (13)CO(2) recovery from (13)C-MTG at 6 hours decreased from 84.5% +/- 7.8% to 42.0% +/- 1.5% of the dose (0 mg and 800 mg of orlistat per kilogram of chow, respectively; P <.001). The 6-hour recovery of breath (13)CO(2) appeared to be highly correlated with the percentage of fat absorption (r = 0.88, P <.001). In rats with fat absorption higher than 70%, however, the coefficient of variation of the (13)C-MTG breath test was 3-fold larger than that of the fat balance.

CONCLUSIONS

The (13)C-MTG breath test could potentially replace the fat balance method for comparing fat absorption efficacy between groups. Yet, a considerable interindividual variation of the (13)C-MTG breath test under conditions of relatively mild fat malabsorption does not support its application for diagnostic purposes in individuals.