Role of hepatic fatty acid:coenzyme A ligases in the metabolism of xenobiotic carboxylic acids

1. Formation of acyl-coenzymes (Co)A occurs as an obligatory step in the metabolism of a variety of endogenous substrates, including fatty acids. The reaction is catalysed by ATP-dependent acid:CoA ligases (EC 6.2.1.1-2.1.3; AMP forming), classified on the basis of their ability to conjugate saturated fatty acids of differing chain lengths, short (C2-C4), medium (C4-C12) and long (C10-C22). The enzymes are located in various cell compartments (cytosol, smooth endoplasmic reticulum, mitochondria and peroxisomes) and exhibit wide tissue distribution, with highest activity associated with liver and adipose tissue. 2. Formation of acyl-CoA is not unique to endogenous substrates, but also occurs as an obligatory step in the metabolism of some xenobiotic carboxylic acids. The mitochondrial medium-chain CoA ligase is principally associated with metabolism via amino acid conjugation and activates substrates such as benzoic and salicylic acids. Although amino acid conjugation was previously considered an a priori route of metabolism for xenobiotic-CoA, it is now recognized that these highly reactive and potentially toxic intermediates function as alternative substrates in pathways of intermediary metabolism, particularly those associated with lipid biosyntheses. 3. In addition to a role in fatty acid metabolism, the hepatic microsomal and peroxisomal long-chain-CoA-ligases have been implicated in the formation of the acyl-CoA thioesters of a variety of hypolipidaemic and peroxisome proliferating agents (e.g. clofibric acid) and of the R(-)-enantiomers of the commonly used 2-arylpropionic acid non-steroidal anti-inflammatory drugs (e.g. ibuprofen). In vitro kinetic studies using rat hepatic microsomes and peroxisomes have alluded to the possibility of xenobiotic-CoA ligase multiplicity. Although cDNA encoding a long-chain ligase have been isolated from rat and human liver, there is currently no molecular evidence of multiple isoforms. The gene has been localized to chromosome 4 and homology searches have revealed a significant similarity with enzymes of the luciferase family. 4. Increasing recognition that formation of a CoA conjugate increases chemical reactivity of xenobiotic carboxylic acids has led to an awareness that the relative activity, substrate specificity and intracellular location of the xenobiotic-CoA ligases may explain differences in toxicity. 5. Continued characterization of the human xenobiotic-CoA ligases in terms of substrate/inhibitor profiles and regulation, will allow a greater understanding of the role of these enzymes in the metabolism of carboxylic acids.     

Essential fatty acid deficiency in well nourished young cystic fibrosis patients

Essential fatty acid deficiency is well known in cystic fibrosis patients, but its pathogenesis remains unclear. It might be related to protein-energy malnutrition which is a common feature of cystic fibrosis or to some specific defects in fatty acid metabolism. To avoid the deleterious effects of protein-energy malnutrition, this study assesses the plasma phospholipid fatty acid pattern in well nourished young cystic fibrosis subjects. Sixteen cystic fibrosis subjects aged 6.6-20.0 years were studied and compared to 16 healthy controls matched for gender, age and nutritional status. Plasma phospholipids were separated by thin layer chromatography and phospholipid fatty acid pattern was determined by gas liquid chromatography. Anthropometry and dual-energy X-ray absorptiometry showed that lean body mass, fat-free mass and fat mass were similar in the two groups. Nutritional inquiry showed higher ingestion of macronutrients by cystic fibrosis subjects than by controls. Plasma phospholipid palmitoleic acid and eicosatrienoic acid were higher, and by contrast linoleic acid and docosahexaenoic acid were lower in cystic fibrosis subjects than in controls. The ratio linoleic acid/arachidonic acid was lower and the ratio eicosatrienoic acid/arachidonic acid was higher in cystic fibrosis subjects than in controls. CONCLUSION: Essential fatty acid deficiency is present in young cystic fibrosis subjects in the absence of protein-energy malnutrition. It means that this deficiency is probably related to specific defects in fatty acid metabolism.     

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.     

Colonic strictures in children with cystic fibrosis

PURPOSE: To determine the radiographic, clinical, surgical, and histologic findings in children with cystic fibrosis who develop strictures of the colon. MATERIALS AND METHODS: Ten children (five boys, five girls; age range, 2.5-9.0 years; mean age, 5.5 years), who were treated at the practices of the authors, were retrospectively identified and their medical records reviewed. RESULTS: Radiographic manifestations of the colonic disease included mucosal irregularity and spiculation with nodular thickening of the colonic wall and loss of normal colonic haustration. Luminal narrowing involved long segments of the colon. Longitudinal shortening of the colon was also a prominent feature. The decrease in caliber of the bowel ranged from mild narrowing to complete occlusion of the lumen. Histologic examination revealed severe submucosal fibrosis and fatty infiltration with transmural extension of the fibrosis to involve the serosa in some cases. Unlike in Crohn disease, however, acute inflammatory changes were minimal or absent. CONCLUSION: Colonic stricture in children with cystic fibrosis is due to irreversible and frequently progressive narrowing of the colonic lumen.     

Fibrosing colonopathy in children with cystic fibrosis

PURPOSE: Fibrosing colonopathy is a newly described entity seen in children with cystic fibrosis. The radiological hallmarks are foreshortening of the right colon with varying degrees of stricture formation. High-dose enzyme therapy has been implicated as the cause of this process. The purpose of this study is to review the author's experience with evaluation and treatment of these patients. METHODS: There are currently 380 patients being treated at our CF center. Fifty-five of these patients have been treated with high-dose enzyme therapy (> 5,000 units of lipase/kg). The medical records of these patients, who are at risk for developing fibrosing colonopathy, were reviewed for the presence of recurrent abdominal complaints, and the work-up and treatment of these symptoms. RESULTS: Chronic complaints of abdominal pain, distension, change in bowel habits, or failure to thrive were present in 24 of the 55 patients treated with high-dose enzymes. So far, 18 of these 24 patients have been evaluated by contrast enema. Thirteen of eighteen have been found to have fibrosing colonopathy characterized by foreshortening and strictures of the colon. Additional findings included focal strictures of the right colon (7 of 13), long segment strictures (5 of 13), and total colonic involvement (1 of 13). Nine patients with the most severe symptoms have undergone colon resection, including five segmental right colectomies, three extended colectomies (ileo-sigmoid anastomosis), and one subtotal colectomy with end-ileostomy. Pathological evaluation has shown submucosal fibrosis, destruction of the muscularis mucosa, and eosinophilia. No postoperative complications or deaths occurred. All nine postoperative patients have noted marked symptomatic improvement. Contrast enema follow-up results are available for six patients, and have documented no recurrent strictures to date. Three of four nonoperative patients have less severe symptoms and are currently being treated conservatively. The other family has refused surgery and the patient is being treated symptomatically. CONCLUSION: High-dose lipase replacement has been implicated as the etiology for FC and was present in all of our patients. Our cystic fibrosis center now routinely limits lipase to 2,500 U/kg per dose. We recommend the use of the contrast enemas to evaluate at-risk patients who have chronic abdominal complaints or who present with recurrent bowel obstruction. Colon resection should be performed in those with clinically and radiographically significant strictures with the expectation of a good outcome.     

Effects of fatty acids and hormones on fatty acid metabolism and gluconeogenesis in bovine hepatocytes

Primary cultures of hepatocytes were used to study the effects of extracellular oleate concentration and hormones on fatty acid metabolism and gluconeogenesis. Rates of oleate uptake and oxidation to acid-soluble products varied linearly as oleate concentrations increased (0.1 to 2 mM), but rates of triglyceride accumulation varied quadratically. Insulin increased the proportion of oleate that was esterified by 22% without affecting the formation of acid-soluble products. Cells incubated with 2 mM [1-(14)C]oleate for 24 h eliminated 9.6% of the labeled intracellular lipid as acid-soluble products in the following 24 h when no oleate was present during depletion and eliminated 7.7% when 2 mM oleate was present. Insulin reduced labeled triglyceride depletion by 49%. Gluconeogenesis from [2-(14)C] propionate was depressed by 24%, and formation of acid-soluble products was increased by 46% in cells infiltrated with lipid because of previous exposure to 2 mM oleate for 45 h. Rates of gluconeogenesis from propionate were reduced 23% when 2 mM oleate was present during the 3-h period that gluconeogenesis was measured, and the effect was not modified by lipid infiltration. Lipid infiltration influenced hepatic function, and insulin regulated hepatic triglyceride concentration.     

The effect of 12 months'' treatment with eicosapentaenoic acid in five children with cystic fibrosis

BACKGROUND: The use and indications for laparoscopy have been increasing. As part of this trend, a new algorithm may emerge for pediatric trauma in which laparoscopic techniques are used in hemodynamically stable patients with suspected hollow viscus perforation. CASE REPORT: We present a case in which laparoscopy was successfully used in a pediatric trauma patient as a diagnostic and therapeutic modality. A 4-year-old boy was a back-seat passenger in a head-on collision motor vehicle accident. He was restrained by a lap seat belt. He sustained a concussion, a large forehead laceration and a seat belt abdominal injury. On admission, he complained of abdominal pain. Physical examination revealed a soft, non-distended abdomen with moderate diffuse tenderness. He was hemodynamically stable. Computerized tomography of the abdomen revealed free fluid in the pelvis. No abnormalities were detected in the liver or spleen. Because of clinical deterioration and suspected intestinal perforation, diagnostic laparoscopy was utilized instead of proceeding directly to celiotomy. At laparoscopy a jejunal perforation was found and successfully repaired laparoscopically. Large hematomas were seen in the mesentery, as well as an unsuspected splenic laceration. No active bleeding was found. The patient recovered uneventfully and was discharged 5 days following the surgical procedure. CONCLUSION: This case illustrates the efficacy of using early laparoscopy in children with abdominal trauma when diagnosis is difficult and hollow viscus injury is suspected.     

Specific inhibition of hepatic fatty acid synthesis exerted by dietary linoleate and linolenate in essential fatty acid adequate rats

Dietary linoleate and linolenate were investigated for their ability to specifically inhibit liver and adipose tissue lipogenesis in meal-fed (access to food 900-1,200 hr), essential fatty acid (EFA) adequate rats. Supplementing a high carbohydrate diet containing 2.5% safflower oil with 3% palmitate 16:0, oleate 18:1, or linoleate 18:2 did not affect in vivo liver or adipose tissue fatty acid synthesis. However, 18:2 addition to the basal diet did result in a significant (P less than 0.05) decline of liver fatty acid synthetase (FAS) and glucose-6-phosphate dehydrogenase (G6PD) activities. When the safflower oil content of the basal diet was reduced to 1%, the addition of 3% 18:2 or linolenate 18:3 significantly (P less than 0.05) depressed hepatic FAS, G6PD, and in vivo fatty acid synthesis by 50%. Addition of 18:1 caused no depression in hepatic FAS activity but did result in a significant (P less than 0.05) decline in liver G6PD activity and fatty acid synthesis which was intermediate between basal and basal +18:2- or +18:3-fed animals. Adipose tissue rates of lipogenesis were completely unaffected by dietary fatty acid supplementation. Similarly, the addition of 3 or 5% 18:3 to a basal diet for only one meal resulted in no change in lipogenesis relative to that in animals fed the basal diet. The data indicate that, like rats fed EFA-deficient diets, dietary 18:2 and 18:3 exert a specific capacity to depress rat liver FAS and G6PD activities and rate of fatty acid synthesis.     

The effect of under- and overnutrition on essential fatty acid metabolism in childhood

Intermittent catheterisation is suitable for a range of patients and has a high level of patient satisfaction. Careful education is required to minimise the risk of complications and nurses should be aware of the various types of catheter available.     

Effect of essential and nonessential fatty acids in complex mixture on fatty acid composition of liver lipids

Linoleate, linolenate, arachidonate, docosahexenoate and six other fatty acids were major components of 24 ester preparations fed as 5% of the diet for 60 days to groups of male white rats. The experiment was designed so as to provide that all major fatty acid components were independent of each other in the sense that the intake of each was poorly correlated with the intake of any of the others. Fatty acid compositions of liver lipids were determined and were related to the composition of the diet lipids. Linolenate and docosahexaenoate contents of diet and tissue revealed the same relationships reported previously from experiments in which individual pure acid esters were added to a fat-free diet. Linoleate, when fed in lipid mixtures, was more effective in raising the linoleate concentration in liver lipids than when fed alone, but this increase did not change the shape of the dose-response curve or the estimated nutritional requirement. Large amounts of fish oil in the diet tended to depress the arachidonate concentration in tissue lipids.     

Retrospective review of the effects of rhDNase in children with cystic fibrosis

Bone densitometry is characterized by high sensitivity and specificity in osteoporosis, and new generations of densitometers enable measurements with improved intra- and inter-assay precision. The clinical potential of bone densitometry is well documented and the technique is widely used in clinical practice. It does not, however, allow for measurement of "true" bone density; instead it measures so called serial density (expressed in g/cm2) which is the distribution of bone mass over the flat projection of the skeleton. Limitations of densitometric techniques can be overcome by applying other methods, i.e. quantitative computed tomography (QCT) and ultrasound (US). QCT enables separate measurements of compact and trabecular bone density (expressed in g/cm3), as well as calculation of Strength-Strain Index (SSI), reflecting the mechanical resistance of bone to fracture. US is a non-invasive technique, providing information of fracture risk and bone tissue quality. Both techniques seem very promising and have been extensively studied recently; they are expected to move from clinical research to clinical practice soon.     

Correlates of well-being in mothers of children and adolescents with cystic fibrosis

The phytoestrogen, genistein, is a naturally occurring isoflavone found in soy products. On a biochemical basis, genistein is a competitive inhibitor of tyrosine kinases and the DNA synthesis-related enzyme, topoisomerase-II (topo-II). Exposure of mammalian cells to genistein results in DNA damage that is similar to that induced by the topo-II inhibitor and chromosomal mutagen, m-amsa. In order to determine the potential genotoxicity of genistein, human lymphoblastoid cells which differ in the functional status of the tumor suppressor gene, p53, were exposed to genistein and the induction of micronuclei quantified by microscopic analysis. In addition, the mutant fraction at the thymidine kinase (tk) locus (both the normal-growth and slow-growth phenotypes) was determined by resistance to trifluorothymidine (TFT) and at the hypoxanthine phosphoribosyl transferase (hprt) locus by resistance to 6-thioguanine (6-TG). Flow cytometric analysis of the percentage of viable, apoptotic and degenerating cells was utilized to determine the rate and kinetics of cell death after genistein exposure. The detection of micronuclei in both cell lines indicated that genistein-induced damage had occurred in both AHH-1 tk+/- and L3. Linear regression analysis detected a significant increase in the number of 6-TG-resistant clones in both AHH-1 tk+/- (p53+/-) and L3 (p53+/+). A comparison of slopes revealed no difference between the lines. In contrast, a significant, concentration-dependent increase in the number of TFT-resistant clones with the slow-growth phenotype was detected in AHH-1 tk+/- (mutant p53), but not in L3 (wild-type p53). Cell death occurred primarily by apoptosis in both cell lines; however, a concentration-dependent decrease in the percentage of viable cells was detected immediately after exposure in L3, but not until 32 h after exposure in AHH-1 tk+/-. A comparison of the slopes of the concentration-response curves for the percentage of viable cells revealed no difference between the cell lines in the effect of genistein on cell viability. Our results may be interpreted that genistein is a chromosomal mutagen and that p53 functional status affects the recovery of chromosomal mutants, possibly by signalling cells into the apoptosis pathways.     

Acute modulation of rat hepatic lipid metabolism by sulphur-substituted fatty acid analogues

A single oral dose of two 3-thia (3-thiadicarboxylic and tetradecylthioacetic acids) and of 4-thia (tetradecylthiopropionic acid) fatty acids were administered to normolipidemic rats and their effects on lipid metabolism over a 24 hr period were studied. All three thia fatty acids could be detected in plasma 2 hr after treatment. Tetradecylthioacetic and tetradecylthiopropionic acids were detected in different hepatic lipid fractions but were incorporated mainly into hepatic phospholipids. Two hours after administration hepatic mitochondrial beta-oxidation and the total liver level of long-chain fatty acyl-CoA increased with a concomitant decrease in saturated fatty acids, total hepatic malonyl-CoA and plasma triacylglycerol levels in the 3-thia fatty acid groups. Tetradecylthiopropionic acid administration caused a decrease in mitochondrial beta-oxidation and an increase in plasma triacylglycerol at 24 hr. The activities of key lipogenic enzymes were unaffected in all treatment groups. Plasma cholesterol level was reduced only at 8 hr in 3-thiadicarboxylic acid treated rats although 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase was suppressed already at 2, 4, 8 and 12 hr. The results show that thia fatty acids are rapidly absorbed and are systemically available after oral administration but the 3-thia fatty acids reached systemic circulation more slowly and less completely than the 4-thia fatty acid. Very low levels of the thia fatty acids are detected in plasma 24 hr after a single administration. They are incorporated into all hepatic lipid classes, especially phospholipids. Rapid incorporation of a non beta-oxidizable thia fatty acid into hepatic lipids may cause a diversion of other fatty acids from glycerolipid biosynthesis to mitochondrial beta-oxidation. Stimulation of mitochondrial beta-oxidation and suppression of HMG-CoA reductase are primary events, occurring within hours, after 3-thia fatty acid administration. The hypotriglyceridemic effect of the 3-thia fatty acids observed at 2-4 hr is independent of the activities of key lipogenic and triacylglycerol synthesising enzymes.     

Effects of feeding on protein turnover in healthy children and in children with cystic fibrosis

In 24 patients presenting with 55 renal lesions (mean size, 20.8 mm), single-breath-hold (SBH) fast spin-echo (FSE) techniques allowing T1 and T2 images to be produced within 20 and 23 sec, respectively, were compared with routine non-breath-hold (NBH) spin-echo (SE) T1 and NBH-FSE T2 sequences. Contrast-to-noise ratios (CNRs) measured from SBH-FSE T1 images were an average of 97% higher than their NBH counterparts (P = .0001) and allowed an improved lesion conspicuity in 80% of the cases (P = 0.0001). For T2 imaging, SBH-FSE and NBH-FSE sequences were not statistically different with respect to lesion conspicuity (P = .55) and CNR values (P = .19). This was observed despite a 35% average decrease in CNR of SBH-FSE compared to NBH-FSE images. By reducing respiratory motion artifacts while preserving SE-like image contrast, SBH-FSE techniques have the potential to replace routine NBH sequences for an optimal diagnosis of renal masses.     

Determinants of the tension-time index of inspiratory muscles in children with cystic fibrosis

1. Hypertension secondary to renal disease was studied in non-pregnant and pregnant ewes to determine whether there were any changes in arterial pressure and the distribution of cardiac output and, in particular, whether uteroplacental blood flow was affected. 2. In six non-pregnant, chronically catheterized, uninephrectomized ewes, a reduction in renal blood flow (RBF) to 40-50% of control caused hypertension within 3 h. This was maintained for as long as RBF was reduced (72 h) and returned to control 24 h after the occluder around the renal artery was released. When this experiment was repeated in 16 uninephrectomized pregnant ewes (118-134 days gestation) hypertension occurred within 3 h and was sustained for as long as RBF was reduced (between 24 and 72 h). Arterial pressure returned to control within 24-72 h of restoring RBF. 3. Compared with non-pregnant ewes, pregnant ewes had similar arterial pressures, higher cardiac outputs (CO; P < 0.001) and heart rates (HR; P < 0.001), lower total peripheral resistances (TPR; P < 0.001) and similar blood flows to brain, ovary, pancreas, kidney and spleen. Splenic vascular resistance (VR) was greater (P = 0.006), gut blood flow was greater (P < 0.05) and gut VR was less (P < 0.05). Myoendometrial blood flow/g was greater (P < 0.005) and myoendometrial VR was less (P = 0.006). 4. In pregnant sheep with renal clip hypertension, there was no change in CO and HR, but TPR increased (P < 0.01), as did plasma renin activity. Gut, brain, pancreatic and myoendometrial VR were increased as long as RBF was reduced; in addition, myoendometrial VR remained high for the rest of the experiment. Placental blood flow was unchanged at 3 h; 24-72 h later it was reduced (P < 0.05) and remained low. Placental VR was increased 24-72 h after RBF was restored when ewes were again normotensive. 5. Thus, one-clip, one-kidney renal hypertension in the pregnant ewe was due to increased TPR associated with a fall in uteroplacental blood flow that persisted even when RBF was restored and ewes were normotensive. This reduction in uteroplacental blood flow could account for the high foetal morbidity and mortality that occurs in pregnant women with renovascular hypertension.