Jan I. Pedersen

Metabolic aspects of peroxisomal β-oxidation

In the course of the last decade peroxisomal beta-oxidation has emerged as a metabolic process indispensable to normal physiology. Peroxisomes beta-oxidize fatty acids, dicarboxylic acids, prostaglandins and various fatty acid analogues. Other compounds possessing an alkyl-group of six to eight carbon atoms (many substituted fatty acids) are initially omega-oxidized in endoplasmic reticulum. The resulting carboxyalkyl-groups are subsequently chain-shortened by beta-oxidation in peroxisomes. Peroxisomal beta-oxidation is therefore, in contrast to mitochondrial beta-oxidation, characterized by a very broad substrate-specificity. Acyl-CoA oxidases initiate the cycle of beta-oxidation of acyl-CoA esters. The next steps involve the bi(tri)functional enzyme, which possesses active sites for enoyl-CoA hydratase-, beta-hydroxyacyl-CoA dehydrogenase- and for delta 2, delta 5 enoyl-CoA isomerase activity. The beta-oxidation sequence is completed by a beta-ketoacyl-CoA thiolase. The peroxisomes also contain a 2,4-dienoyl-CoA reductase, which is required for beta-oxidation of unsaturated fatty acids. The peroxisomal beta-hydroxyacyl-CoA epimerase activity is due to the combined action of two enoyl-CoA hydratases. (For a recent review of the enzymology of beta-oxidation enzymes see Ref. 225.) The broad specificity of peroxisomal beta-oxidation is in part due to the presence of at least two acyl-CoA oxidases, one of which, the trihydroxy-5 beta-cholestanoyl-CoA (THCA-CoA) oxidase, is responsible for the initial dehydrogenation of the omega-oxidized cholesterol side-chain, initially hydroxylated in mitochondria. Shortening of this side-chain results in formation of bile acids and of propionyl-CoA. In relation to its mitochondrial counterpart, peroxisomal beta-oxidation in rat liver is characterized by a high extent of induction following exposure of rats to a variety of amphipathic compounds possessing a carboxylic-, or sulphonic acid group. In rats some high fat diets cause induction of peroxisomal fatty acid beta-oxidation and of trihydroxy-5 beta-cholestanoyl-CoA oxidase. Induction involves increased rates of synthesis of the appropriate mRNA molecules. Increased half-lives of mRNA- and enzyme molecules may also be involved. Recent findings of the involvement of a member of the steroid hormone receptor superfamily during induction, suggest that induction of peroxisomal beta-oxidation represents another regulatory phenomenon controlled by nuclear receptor proteins. This will likely be an area of intense future research. Chain-shortening of fatty acids, rather than their complete beta-oxidation, is the prominent feature of peroxisomal beta-oxidation.(ABSTRACT TRUNCATED AT 400 WORDS)

Can vitamin D supplementation reduce the risk of fracture in the elderly? A randomized controlled trial.

Randomized controlled trials have shown that a combination of vitamin D and calcium can prevent fragility fractures in the elderly. Whether this effect is attributed to the combination of vitamin D and calcium or to one of these nutrients alone is not known. We studied if an intervention with 10 μg of vitamin D3 per day could prevent hip fracture and other osteoporotic fractures in a double‐blinded randomized controlled trial. Residents from 51 nursing homes were allocated randomly to receive 5 ml of ordinary cod liver oil (n = 569) or 5 ml of cod liver oil where vitamin D was removed (n = 575). During the study period of 2 years, fractures and deaths were registered, and the principal analysis was performed on the intention‐to‐treat basis. Biochemical markers were measured at baseline and after 1 year in a subsample. Forty‐seven persons in the control group and 50 persons in the vitamin D group suffered a hip fracture. The corresponding figures for all nonvertebral fractures were 76 persons (control group) and 69 persons (vitamin D group). There was no difference in the incidence of hip fracture (p = 0.66, log‐rank test), or in the incidence of all nonvertebral fractures (p = 0.60, log‐rank test) in the vitamin D group compared with the control group. Compared with the control group, persons in the vitamin D group increased their serum 25‐hydroxyvitamin D concentration with 22 nmol/liter (p = 0.001). In conclusion, we found that an intervention with 10 μg of vitamin D3 alone produced no fracture‐preventing effect in a nursing home population of frail elderly people.

Factors Associated with Mortality after Hip Fracture

Abstract: There is a well-known excess mortality subsequent to hip fracture, which is probably restricted to subgroups of hip fracture patients with reduced health status. We studied the association between risk factors and death in 248 hip fracture patients and 248 controls originally enrolled in a population-based case–control study. This cohort was followed for 3 1/2 years with respect to total mortality. A markedly increased mortality was found in hip fracture patients passing a mental status test at a low score [relative risk (RR) = 2.3, 95% confidence interval (CI) 1.4-3.7], in hip fracture patients reporting two or more selected chronic diseases (RR = 3.3, 95% CI 1.8–6.1), in hip fracture patients not walking outdoors before the fracture (RR = 3.2, 95% CI 2.0–5.1) and in hip fracture patients in the lower half of handgrip strength distribution (RR = 2.3, 95% CI 1.6–3.4), all compared with the control group. In contrast, hip fracture patients without these risk factors did not have increased mortality compared with the control group. This study suggests that otherwise healthy and fit patients do not have increased mortality subsequent to hip fracture. The excess mortality is restricted to persons with reduced mental status, reduced somatic health and low physical ability. Special attention should be paid to patients with such risk factors in the treatment and rehabilitation period.

Conversion of 3α,7α,12α-trihydroxy-5β-cholestanoic acid into cholic acid by rat liver peroxisomes

3a,7ar,l2o-Trihydroxy-SP-cholestanoic acid (THCA) is considered to be a precursor for cholic acid formation [l]. 3a,7a,l2cr,24-Tetrahydroxy-5/3cholestanoic acid is a probable intermediate in the reaction [2-4]. 24-Hydroxylation of THCA has been shown to be catalyzed by the mitochondrial fraction of rat liver in combination with the 100 000 X g supematant fluid [4,5]. The microsomal fraction in combination with the 100 000 X g supernatant and ATP also catalyzes 24hydroxylation [4] and the reaction was shown to be due to the combined action of a desaturase and a hydratase [4]. The final thiolytic cleavage of the side chain in cholic acid formation [6] has been shown to be catalyzed by the mitochondrial fraction [3 5 ;I], the soluble fraction [3,5], or by a combination of the microsomal fraction and the 100 000 X g supernatant [7]. The over-all formation of cholic acid from THCA in the mitochondrial fraction is dependent on the presence of ATP, coenzyme A, NAD and Mg2+ in the reaction medium [5 ;I]. It thus appears that this reaction has certain features in common with the Poxidation of fatty acids. Recently, a fatty acid oxidizing system different from the one present in the mitochondria has been identified in the peroxisomal fraction of both rat [8,9] and human [lo] liver. On the basis of these findings the subcellular localization of cholic acid formation has been further investigated. This work shows that the peroxisomal fraction of rat liver is able to catalyze the conversion of THCA into cholic acid.

Dairy products and metabolic effects in overweight men and women: results from a 6-mo intervention study

BACKGROUND Some epidemiologic studies have suggested inverse relations between intake of dairy products and components of the metabolic syndrome. OBJECTIVE The objective was to investigate the effects of an increased intake of dairy products in persons with a habitually low intake on body composition and factors related to the metabolic syndrome. DESIGN Middle-aged overweight subjects (n = 121) with traits of the metabolic syndrome were recruited in Finland, Norway, and Sweden and randomly assigned into milk or control groups. The milk group was instructed to consume 3-5 portions of dairy products daily. The control group maintained their habitual diet. Clinical investigations were conducted on admission and after 6 mo. RESULTS There were no significant differences between changes in body weight or body composition, blood pressure, markers of inflammation, endothelial function, adiponectin, or oxidative stress in the milk and the control groups. There was a modest unfavorable increase in serum cholesterol concentrations in the milk group (P = 0.043). Among participants with a low calcium intake at baseline (<700 mg/d), there was a significant treatment effect for waist circumference (P = 0.003) and sagittal abdominal diameter (P = 0.034). When the sexes were analyzed separately, leptin increased (P = 0.045) and vascular cell adhesion molecule-1 decreased (P = 0.001) in women in the milk group. CONCLUSIONS This study gives no clear support to the hypothesis that a moderately increased intake of dairy products beneficially affects aspects of the metabolic syndrome. The apparently positive effects on waist circumference and sagittal abdominal diameter in subjects with a low calcium intake suggest a possible threshold in relation to effects on body composition.

Trans10, cis12-conjugated linoleic acid prevents triacylglycerol accumulation in adipocytes by acting as a PPARγ modulator

A group of polyunsaturated fatty acids called conjugated linoleic acids (CLAs) are found in ruminant products, where the most common isomers are cis9, trans11 (c 9,t11) and trans10, cis12 (t10,c12) CLA. A crude mixture of these isomers has been shown in animal studies to alter body composition by a reduction in body fat mass as well as an increase in lean body mass, with the t10,c12 isomer having the most pronounced effect. The objective of this study was to establish the molecular mechanisms by which t10,c12 CLA affects lipid accumulation in adipocytes. We have shown that t10,c12 CLA prevents lipid accumulation in human and mouse adipocytes at concentrations as low as 5 μM and 25 μM, respectively. t10,c12 CLA fails to activate peroxisome proliferator-activated receptor γ (PPARγ) but selectively inhibits thiazolidinedione-induced PPARγ activation in 3T3-L1 adipocytes. Treatment of mature adipocytes with t10,c12 CLA alone or in combination with Darglitazone down-regulates the mRNA expression of PPARγ as well as its target genes, fatty acid binding protein (aP2) and liver X receptor α (LXRα). Taken together, our results suggest that the trans10, cis12 CLA isomer prevents lipid accumulation in adipocytes by acting as a PPARγ modulator.

Mapping of the Locus for Cholestasis-Lymphedema Syndrome (Aagenaes Syndrome) to a 6.6-cM Interval on Chromosome 15q

Patients with cholestasis-lymphedema syndrome (CLS) suffer severe neonatal cholestasis that usually lessens during early childhood and becomes episodic; they also develop chronic severe lymphedema. The genetic cause of CLS is unknown. We performed a genome screen, using DNA from eight Norwegian patients with CLS and from seven unaffected relatives, all from an extended pedigree. Regions potentially shared identical by descent in patients were further characterized in a larger set of Norwegian patients. The patients manifest extensive allele and haplotype sharing over the 6.6-cM D15S979-D15S652 region: 30 (83.3%) of 36 chromosomes of affected individuals carry a six-marker haplotype not found on any of the 32 nontransmitted parental chromosomes. All Norwegian patients with CLS are likely homozygous for the same disease mutation, inherited from a shared ancestor.

A comparison of the effects of cheese and butter on serum lipids, haemostatic variables and homocysteine.

Milk fat contains considerable amounts of saturated fatty acids, known to increase serum cholesterol. Little is known, however, about the relative effect of different milk products on risk factors for CHD. The aim of the present study was to compare the effects of Jarlsberg cheese (a Norwegian variety of Swiss cheese) with butter on serum lipoproteins, haemostatic variables and homocysteine. A controlled dietary study was performed with twenty-two test individuals (nine men and thirteen women) aged 23-54 years. The subjects consumed three isoenergetic test diets, with equal amounts of fat and protein, and containing either cheese (CH diet), butter + calcium caseinate (BC diet) or butter + egg-white protein (BE diet). The study was a randomised cross-over study and the subjects consumed each diet for 3 weeks, with 1 week when they consumed their habitual diet in between. Fasting blood samples were drawn at baseline and at the end of each period. Serum was analysed for lipids and plasma for haemostatic variables and homocysteine. Total cholesterol was significantly lower after the CH diet than after the BC diet (-0.27 mmol/l; P=0.03), while the difference in LDL-cholesterol was found to be below significance level (-0.22 mmol/l; P=0.06). There were no significant differences in HDL-cholesterol, triacylglycerols, apo A-I, apo B or lipoprotein (a), haemostatic variables and homocysteine between the diets. The results indicate that, at equal fat content, cheese may be less cholesterol increasing than butter.

Risk factors for hip fracture in a high incidence area: a case-control study from Oslo, Norway

The aim of this population-based matched case-control study was to evaluate the effect of risk factors for hip fracture in Oslo, Norway, which has some of the highest incidence rates ever reported. The study population comprised all non-institutionalized persons 50 years or older living in the catchment area of two Oslo hospitals, and cases were 246 patients admitted for hip fracture during a 1-year period. The controls were randomly selected from the study population, matched 1:1 for age and sex. Hip fracture was associated with lean body stature, smoking, low grip strength and decreased levels of physical activity, and inversely with length of education. In addition, hip fracture was inversely related to indicators of total food intake (number of meals per day, frequency of dinners, and slices of bread per day). A relation between hip fracture and low vitamin D intake was also suggested, whereas no association with dietary calcium intake was found. Finally, increased risk of fracture was seen in persons reporting two or more hospital admissions in the previous 2 years, and in those reporting weight reduction due to poor appetite during the previous year. In conclusion, the risk factor pattern for hip fracture was much the same in the elderly population of Oslo as previously described in other populations with a lower incidence of fracture. This study also indicates a relation between hip fracture and low food intake.

Adipose tissue fatty acids and risk of myocardial infarction--a case-control study.

Objectives: To study the association between content in adipose tissue of very long-chain n-3 fatty acids, trans fatty acids, linoleic acid and α-linolenic acid and risk of a first myocardial infarction.Design and subjects: A case-control design among 100 patients and 98 population controls both men and postmenopausal women, age 45–75 y. Adipose tissue fatty acids were determined by gas–liquid chromatography. Intake data were obtained through interview using a validated food frequency questionnaire.Results: Dietary intake and adipose tissue content of the fatty acids studied correlated significantly. Adipose tissue contents of eicosapentaenoic acid (20:5n-3), docosapentaenoic acid (22:5n-3) and docosahexaenoic acid (22:6n-3) were significantly lower while those of trans fatty acids, linoleic and α-linolenic acid were significantly higher in patients than in controls. Age and sex adjusted odds ratios (OR) were significantly reduced with increasing quintiles of very long-chain n-3 fatty acids, thus the OR in the fifth compared to the first quintile was 0.23 (95% CI 0.08–0.70). After further adjustment for waist-to-hip ratio, smoking, family history of CHD and content of trans fatty acids, the OR in the highest quintile was 0.17 (95% CI 0.04–0.76) and the P for trend 0.016. Age and sex adjusted OR was increased in the fifth compared to the first quintile of trans fatty acids (OR 2.81, 95% CI 1.16–6.84), linoleic acid (OR 2.10, 95% CI 0.87–5.07) and α-linolenic acid (OR 1.96, 95% CI 0.83–4.61), and P for trend was 0.002, 0.005 and 0.020, respectively. The trends remained significant after adjustment for waist-to-hip ratio, smoking, and family history of coronary heart disease. Trans fatty acids, linoleic acid and α-linolenic acid in adipose tissue were strongly correlated, indicating a common source, most likely margarine. When each of these fatty acid species were adjusted for the two others the trends were no longer significant.Conclusion: Intake of very long-chain n-3 fatty acids as reflected in adipose tissue content is inversely associated with risk of myocardial infarction. Trans fatty acids, linoleic and α-linolenic acid were intercorrelated and associated with increased risk. It is suggested that the increased risk may be connected to trans fatty acids or to some other factor associated with margarine consumption.Sponsorship: Throne Holsts Foundation for Nutrition Research, The Norwegian Association of Margarine Producers, DeNoFa Fabriker A/S, Tine Norwegian Dairies.European Journal of Clinical Nutrition 54, 618–625.