Plant-based diets contribute to lower circulating leptin in healthy subjects independently of BMI

Much research has shown how important role leptin - a hormone secreted by adipose tissue - plays in the regulation of human body weight, mainly due to its appetite-decreasing effects. Under the conditions of energy balance, leptin is an indicator of the amount of triglycerides stored in adipose tissue. In contrast, in a state of hunger or overeating, it acts as an energy balance sensor, and when its level is too high, it fails to reduce food intake, disturbing maintenance of the proper body mass. Recent studies indicate that there is a relationship between a vegetarian diet and the decreased incidence of cardiovascular diseases, certain types of cancer and obesity. It has been noted that people on plant-based diets have lower body weight and percentage of body fat than omnivores. The aim of the study was to analyze the relationship between serum leptin concentrations and the type of diet. The 143 female volunteers on a vegetarian, vegan or omnivore diet were enrolled in the study. All participants had normal body weight (BMI≥18.5<24.9kg/m2). There were statistically significant differences in the serum leptin concentrations of the studied women. Both in the group of vegetarians and vegans circulating leptin was significantly lower (p<0.001) than in the group of omnivores, with the lack of differences in neither BMI nor in body fat content. This suggests that leptin levels are affected not only by the amount of stored fat, but also by the consumed food. This observation indicates the health-promoting properties of plant diets, by influencing circulating leptin.

Expanded Role of a Dietitian in Monitoring a Gluten-Free Diet in Patients with Celiac Disease: Implications for Clinical Practice

Access to a registered dietitian experienced in celiac disease (CD) is still limited, and consultation when available focuses primarily on the elimination of gluten from the diet. Thus, the aim of this study was to evaluate the nutritional value of a gluten-free diet (GFD) in adult CD patients before, and one year after, the standard dietary education. The study included 72 CD patients on a GFD and 30 healthy controls. The dietary intake of both groups was assessed through a 3-day food diary, while adherence to a GFD in celiac subjects was assessed using Standardized Dietician Evaluation (SDE). Subsequently, all CD patients received detailed education on gluten sources, and 48 of them participated in a one-year follow-up. Results: Comparison with the control group showed that consumption of plant protein in CD patients was significantly lower, whereas fat and calories were higher. At baseline, only 62% of CD patients adhered to a GFD, but the standard dietary education successfully improved it. However, the nutritional value of a GFD after one year did not change, except for a reduced sodium intake. The CD subjects still did not consume enough calcium, iron, vitamin D, folic acid or fiber. In conclusion, while the standard dietary education improved GFD adherence, it did not significantly alter its nutritional value. Therefore, it is necessary to increase the role of a dietitian in the treatment of CD.

Gut microbiome dysbiosis in anorexia nervosa

Anorexia nervosa (AN) is described as an eating disorder, which is characterized by malnutrition, a fear of gaining body mass, and a disturbed self-body image. This disease is dependent on biological, psychological and socio-cultural factors. Among the various biological factors, the importance of intestinal microbiota has recently attracted much attention. Identification of the gut microbiota dysbiosis in patients with AN has opened new and promising research directions. Recent observations focus in particular on the association between intestinal microorganisms and the occurrence of functional gastrointestinal disorders associated with anorexia, anxiety and depression, as well as the regulation of eating habits. The composition of the gut microbiota differs between patients with AN and individuals with normal body mass. This is due to the incorrect diet of patients; on the other hand, there is growing interest in the role of intestinal microbiota in the pathogenesis of AN, its changes through re-nutrition practices, and in particular the modulation of intestinal microbiological composition by means of nutritional interventions or the use of preand probiotics as standard supplements therapy of eating disorders. There is a need for further research about the microbiome - intestine - brain axis. Furthermore, consequences of changes in dietary habits as part of AN treatment are also unknown. However, better knowledge about the relationship between the gut microbiome and the brain can help improve the treatment of this disorder. This review aims to present the current knowledge about the potential role of intestinal microbiota in the pathogenesis, course and treatment of AN.

Impact of diet and synbiotics on selected gut bacteria and intestinal permeability in individuals with excess body weight - A Prospective, Randomized Study

Overweight and obese individuals may have leaky intestinal barrier and microbiome dysbiosis. The aim of this study was to determine whether body mass reduction with diet and synbiotics in an adult person with excess body mass has an influence on the gut microbiota and zonulin concentration. The study was a single blinded trial. 60 persons with excess body mass were examined. Based on randomization, patients were qualified either to the intervention group (Synbiotic group) or to the control group (Placebo group). Anthropometric measurements, microbiological assessment of faecal samples and zonulin concentration in the stool were performed before and after observation. After 3-months, an increase in the variety of intestinal bacteria (increase in the Shannon-Weaver index and the Simpson index) and a decrease in concentration of zonulin in faecal samples were observed in the Synbiotic group. Also, statistically significant correlation between zonulin and Bifidobacterium spp. (Spearman test, R=-0.51; p=0.0040) was noticed. There were no significant relationships between the body mass, BMI and changes in the intestinal microbiota or zonulin concentrations. The use of diet and synbiotics improved the condition of the microbiota and intestinal barrier in patients in the Synbiotic group.

Vitamin D in edible mushrooms: biosynthesis, contents, bioavailability, and nutritional significance

Edible mushrooms exposed to sunlight or UV irradiation convert ergosterol to ergocalciferol (vitamin D₂), which is well absorbed and has a similar bioavailability to vitamin D₃. Consumption of vitamin D₂ – enhanced mushrooms significantly increases circulating levels of 25-hydroxyvitamin D₂ that is further metabolized to the biologically active form – 1,25(OH)₂D₂. Dietary supplementation with UV-irradiated mushrooms has been shown to lower parathyroid hormone (PTH) concentrations in the blood and to increase bone mineral density, to suppress an immune response, to decrease circulating plasminogen activator inhibitor 1 (PAI-1) levels, as well as to improve cognitive performance in dementia syndromes. Current evidence indicates that more than half of the world’s population is vitamin D deficient, mushrooms enriched with ergocalciferol may therefore prove useful as a natural dietary source of this vitamin – incorporating them into the diet can help meet the body’s daily requirement and restore vitamin D status.

Salvia hispanica (chia) as a promising source of n-3 polyunsaturated fatty acids with antiatherogenic and cardioprotective properties

Chia (Salvia hispanica L.) is an annual plant that belongs to the Lamiaceae family. It is native to Mesoamerica, today’s Mexico and Guatemala, where it has been cultivated since ancient times. Chia seed contains up to 18% α-linolenic acid (ALA, 18:3), which constitutes about 60% of total fatty acids, making S. hispanica one of the richest plant sources of this essential fatty acid. ALA, an n-3 polyunsaturated fatty acid (PUFA), serves as the precursor of eicosapentaenoic acid (EPA, 20:5) and docosahexaenoic acid (DHA, 22:6), long-chain n-3 PUFAs that exert the antiatherogenic and cardioprotective effects. In humans, consumption of chia seeds leads to an increase in plasma ALA and EPA levels, and stimulates endogenous DHA synthesis. Among the beneficial effects of chia seed supplementation is also a reduction in total cholesterol and VLDL cholesterol with a concomitant increase in HDL cholesterol in hyperlipidemic subjects, a significant reduction in the systolic blood pressure (SBP) in hypertensive individuals, an attenuation of postprandial hyperglycemia, and a decrease in plasma levels of C-reactive protein (CRP) – the marker of inflammation. In view of these findings, chia seeds can be considered an important component of a cardioprotective diet.

[Leptin as a mediator between obesity and cardiac dysfunction]

Obesity is now recognised as one of the most important risk factors for heart disease. Obese individuals have high circulating levels of leptin, a hormone secreted by adipose tissue and involved in energy homeostasis. Growing evidence suggests that leptin may contribute to the development of cardiac dysfunction. In a large prospective study leptin has been shown to be an independent risk factor for coronary heart disease. An independent positive association has also been found between plasma leptin levels and heart rate in hypertensive patients and heart transplant recipients. In animal studies chronic leptin infusion increased heart rate and blood pressure. It has also been demonstrated that circulating leptin levels are elevated in patients with heart failure. The level of plasma leptin was associated with increased myocardial wall thickness and correlated with left ventricular mass, suggesting a role for this hormone in mediating left ventricular hypertrophy in humans. Moreover, leptin directly induced hypertrophy and hyperplasia in human and rodent cardiomyocytes, accompanied by cardiac extracellular matrix remodelling. Leptin may also influence energy substrate utilisation in cardiac tissue. These findings suggest that leptin acting directly or through the sympathetic nervous system may have adverse effects on cardiac structure and function, and that chronic hyperleptinaemia may greatly increase the risk of cardiac disorders. Additional studies are needed to define the role of leptin in cardiac physiology and pathophysiology, nevertheless the reduction in plasma leptin levels with caloric restriction and weight loss may prevent cardiac dysfunction in obese patients.

[Trans-fatty acids--effects on coronary heart disease]

Trans-fatty acids (TFA) are formed during the industrial process of hydrogenation of vegetable oils. The consumption of hydrogenated fats has increased significantly over the last few decades. In Poland, the average daily intake of TFA for adults was estimated to be 2.8 to 6.9 g; which greatly exceeds the recommended daily maximum of 2 g/day (less than 1% of total energy intake). Increasing trans-fatty acid intake has detrimental effects on the lipid profile: TFA raise total cholesterol, LDL-cholesterol and triglyceride concentrations, and decrease HDL-cholesterol levels. Moreover, dietary trans-fatty acids may increase plasma levels of lipoprotein (a) and biomarkers of inflammation and endothelial dysfunction. Several studies have demonstrated that a high intake of TFA is associated with an increased risk of coronary heart disease. In addition, TFA consumption has been implicated as an independent risk factor for sudden cardiac arrest. It is therefore necessary to reduce the intake of hydrogenated fats rich in trans-fatty acids in order to minimize the adverse effects of TFA on health.

[Dietary trans-fatty acids and metabolic syndrome]

Trans-fatty acids (TFAs), products of partial hydrogenation of vegetable oils, have become more prevalent in our diet since the 1960s, when they replaced animal fats. TFAs also occur naturally in meat and dairy products from ruminants. There is growing evidence that dietary trans-fatty acids may increase the risk of metabolic syndrome. Several studies have demonstrated adverse effects of TFAs on plasma lipids and lipoproteins. In dietary trials, trans-fatty acids have been shown to raise the total cholesterol/HDL cholesterol ratio and Lp(a) levels in blood. Moreover, a high intake of TFAs has been associated with an increased risk of coronary heart disease. Prospective cohort studies have shown that dietary trans-fatty acids promote abdominal obesity and weight gain. In addition, it appears that TFA consumption may be associated with the development of insulin resistance and type 2 diabetes. The documented adverse health effects of TFAs emphasise the importance of efforts to reduce the content of partially hydrogenated vegetable oils in foods.

Role of adiponectin in the regulation of carbohydrate and lipid metabolism

Adiponectin, an adipocyte-derived plasma protein, has been shown to play an important role in the regulation of fatty acid and glucose metabolism. Adiponectin enhances fatty acid oxidation both in skeletal and cardiac muscle as well as in the liver, thus reducing triglyceride content in these tissues. Moreover, it stimulates glucose uptake by skeletal and cardiac muscle, and inhibits glucose production by the liver; consequently decreasing blood glucose levels. This review focuses on the molecular mechanisms underlying adiponectin effects on carbohydrate and lipid metabolism in skeletal muscle, cardiac muscle and liver.

The effects of weight cycling on serum leptin levels and lipogenic enzyme activities in adipose tissue

Weight cycling is one of the widely used weight reduction strategies; however, the adverse effects of this method include regaining significant amounts of weight. The molecular mechanisms underlying weight gain following cycles of dietary deprivation and refeeding are still poorly understood. One of the possibilities is that repeated loss and gain of weight may promote fat deposition in adipose tissue. To test this hypothesis we investigated serum leptin levels and lipogenic enzyme activities in white adipose tissue (WAT) of male Wistar rats during 12 days of ad libitum feeding following multiple cycles of alternating food deprivation and refeeding. Rats subjected to eight cycles of food deprivation and refeeding (MFR group) showed significantly decreased circulating leptin levels when compared with control rats (nearly 50% decrease in leptin levels, P < 0.01). Throughout 12 days of ad libitum feeding, serum leptin levels increased modestly but remained significantly (24%, P < 0.05) lower than control levels. Fatty acid synthase (FAS) and malic enzyme (ME) activities (chosen as representatives of enzymes directly involved in fatty acid synthesis) were found to be considerably higher in WAT of MFR rats refed for 3 days in comparison to control rats, and remained elevated even after 12 days of refeeding. These observations suggest that the elevation of lipogenic enzyme activities induced by multiple cycles of dietary deprivation followed by refeeding persists for several days, markedly increasing the lipogenic capacity of adipose tissue, which, accompanied by a decrease in circulating leptin levels, may promote weight gain.

Purine metabolism in pigs and humans and its implications for xenotransplantation

We compared concentrations of nucleotide substrates and activities of enzymes of nucleotide metabolism in pig and human blood, heart, and kidney. The most important difference was lower ecto-5-nucleotidase (ESN) activity in both pig hearts and kidney. Furthermore, higher hypoxanthine, inosine, adenine, and uracil, but lower uridine and uric acid concentrations were observed in pig blood as compared to human. A twofold increase in UTP concentration has been observed in pig hearts following 4 h perfusion with human blood. Purine metabolism is an important target for genetic and pharmacological manipulation during xenotransplantations.

Exposure to human blood inactivates swine endothelial ecto-5'-nucleotidase

Ecto-5'-nucleotidase (E5'N) is an extracellular enzyme forming anti-inflammatory and immunosuppressive adenosine. We evaluated whether confrontation of pig heart and endothelial cells with human blood changes the activity of E5'N. Pig hearts were perfused ex vivo with fresh human blood for 4 h. Pig aortic endothelial cells (PAEC) were incubated in vitro with human plasma for 3 h. Ex vivo perfusion of pig heart with fresh human blood resulted in a decrease in E5'N activity to 62% and 61% of initial in wild-type and transgenic pig hearts, respectively. PAEC activity of E5'N decreased to 71% and 50% of initial after 3 h exposure to heat-inactivated and active complement human plasma, respectively, while it remained constant in controls. Pig heart activity of E5'N decreased following exposure to human blood, which may affect adenosine production and exacerbate hyperacute and vascular rejection.

Peroxisome proliferator-activated receptor alpha is downregulated in the failing human heart

Cardiac hypertrophy in humans is associated with a decrease in myocardial fatty acid beta-oxidation (FAO) and accompanying alterations in metabolic gene expression. Flux through the cardiac FAO pathway, which is the principal source of energy production in the adult mammalian heart, is tightly controlled in accordance with energy demands. In rodents, the FAO pathway is under control of a nuclear peroxisome proliferator-activated receptor alpha (PPARalpha?. We sought to delineate the molecular regulatory events involved in the energy substrate preference switch from fatty acids to glucose during cardiac hypertrophic growth in humans. We analysed the amount of PPARalpha protein in human cardiac tissue. PPARalpha protein level was measured in homogenates prepared from left ventricular biopsies taken from five control donor hearts and compared to the amount of this transcription factor in biopsies from five patients with compensated end-stage heart failure (HF) at the time of transplantation. Using Western blot analysis with a monoclonal antibody against human PPARalpha, we observed a significant decrease (54%) in the mean amount of PPARalpha in the group of HF patients compared to that in the donor tissue. This study indicates that the decrease in cardiac PPARalpha transcription factor gene expression observed in the failing human heart could play an important role in a reduction in fatty acid utilisation by the adult heart during cardiac hypertrophy.

[Adiponectin gene polymorphism and protein dysfunction in the development of insulin resistance]

Adiponectin, an adipocyte-secreted protein encoded by the ACDC gene (also known as APM1), has been shown to play an important role in the regulation of fatty acid and glucose metabolism in liver and muscle, where it modulates insulin sensitivity. Adiponectin enhances fatty acid oxidation in liver and muscle, thus reducing triglyceride content in these tissues. Moreover, it stimulates glucose utilization in muscle and inhibits glucose production by the liver, consequently decreasing blood glucose levels. Plasma adiponectin levels are positively correlated with insulin sensitivity in humans. Circulating adiponectin forms a wide range of multimers. Mutations in the ACDC gene result in an impaired multimerization and/or impaired secretion of adiponectin from adipocytes, both linked to the development of insulin resistance and type II diabetes. This review focuses on the molecular mechanisms underlying hypoadiponectinemia associated with the diabetic phenotype. We further discuss the more recent findings that implicate adiponectin multimer formation as an important feature of the biological function of this adipocyte-derived hormone.

[Role of adiponectin--a protein secreted by adipose tissue in preventing atherosclerosis]

Adiponectin is an adipocyte-specific secretory protein, which seems to play a protective role in different models of vascular injury. Adiponectin infiltrates in the subendothelial space of injured vascular walls and suppresses the expression of adhesion molecules on endothelial cells, thus inhibiting the inflammatory processes that occur during the early phases of atherosclerosis. Adiponectin also suppresses lipid accumulation in macrophages and macrophage-to-foam cell transformation. The ability of adiponectin to act as an anti-inflammatory and anti-atherogenic factor has made this novel adipocytokine a promising therapeutic tool for the future.

Lipogenesis in experimental chronic renal failure in rats

Hyperlipidemia is a common occurance in patients with chronic renal failure (CRF) and has been the subject of many clinical and experimental studies. Despite this, the role of lipogenesis in the development of hyperlipidemia is still obscure. The present study is based on a rat model of CRF involving a two-stage subtotal nephrectomy. In this study, we measured the activity of fatty acid synthase (FAS). This is the rate-limiting enzyme of lipogenesis and is present in liver and white adipose tissue (WAT). Using isotopic methods, we also determined the rate of lipogenesis in vivo in liver and WAT. In both liver and WAT, the results of the analyses were similar. In the uremic rats, there was a tendency for the FAS activity to rise. However, the difference was not statistically significant. Furthermore, there was no increase in the rate of lipogenesis in vivo in either tissue. In summary, the results of our study confirm the thesis that lipogenesis does not play a role in the development of hypertriglyceridemia seen in an experimental CRF in rats.

Increase of lipogenic enzyme mRNA levels in rat white adipose tissue after multiple cycles of starvation-refeeding

Recently, we have found that despite the significant reduction of body weight after multiple starvation-refeeding cycles, white adipose tissue (WAT) exhibits surprisingly high rates of lipogenesis and lipogenic enzyme activities. The purpose of this study was to determine the response of WAT lipogenic enzyme mRNAs of rats subjected to multiple cycles of 3 days fasting and 3 days of refeeding. Despite the body weight reduction, significant increase of lipogenic enzymes (ie, fatty acid synthase [FAS], acetyl-coenzyme A [CoA] carboxylase [ACC], adenosine triphosphate (ATP)-citrate lyase [ACL], NADP-linked malic enzyme [ME], and glucose 6-phosphate dehydrogenase [G6PDH]) mRNAs in WAT was found after multiple cycles of starvation-refeeding of rats on standard laboratory diet. These findings, together with the results published recently, indicate that multiple cycles of starvation-refeeding cause the increased lipogenesis in WAT by upregulation of the lipogenic enzymes gene expression.

Low leptin mRNA level in adipose tissue and normoleptinemia in experimental chronic renal failure

BACKGROUND

Anorexia and weight loss frequently accompany chronic renal failure (CRF). Although multiple metabolic changes occur during CRF, a bulk of evidence indicates that the decrease in caloric intake plays a major role in CRF-induced weight loss. Recently, it has been suggested that elevated plasma leptin concentrations could contribute to anorexia and to downregulation of leptin gene expression in CRF patients. However, in some CRF patients, plasma leptin concentrations have been found to be lower than one could expect. Thus we assumed that inhibition of leptin synthesis plays an important role in the regulation of plasma leptin concentrations in CRF patients.

METHODS

To test this assumption, the leptin mRNA level in rat white adipose tissue from ad-libitum-fed control (sham operated), pair-fed control (sham operated) and rats with experimentally induced CRF has been measured by Northern blotting analysis. In addition, serum leptin concentration (by radioimmunoassay) was determined in all three groups of animals.

RESULTS

The results of the present study indicate that in experimental CRF the leptin mRNA level is decreased by about 50% as compared to the sham-operated animals (ad-libitum-fed and pair-fed controls). The mean serum leptin concentration in CRF rats was essentially similar to the leptin concentration in sham-operated ones.

CONCLUSION

The data obtained suggest that in CRF animals the serum leptin concentration might be affected not only by the decrease in leptin removal in the kidney, but also by the decrease in leptin secretion from adipose tissue. Furthermore, the results of the study suggest that leptin may be only one of many factors involved in the pathogenesis of malnutrition associated with CRF.

The decrease of rat postprandial plasma triacylglycerol concentration after multiple cycles of starvation-refeeding

The effect of multiple cycles of starvation-refeeding on rat body weight and on plasma lipid concentration was studied. After 1 cycle of starvation-refeeding, the rat body weight did not change significantly; however the postprandial plasma triacylglycerol concentration decreased approximately 2-fold as compared to rats fed ad libitum. After 8 cycles of starvation-refeeding, both rat body weight and plasma triacylglycerols concentration decreased. In contrast, the plasma cholesterol (both total and HDL cholesterol) concentration did not change appreciably either after 1 or 8 cycles of starvation-refeeding as compared to control. Although the postprandial plasma triacylglycerol concentration decreased in both groups (i.e. after 1 and 8 cycles of starvation-refeeding), this phenomenon appears to last longer after 8 cycles of starvation-refeeding. The epididymal white adipose tissue weight decreased after both 1 and 8 cycles of starvation-refeeding. After 1 cycle of starvation-refeeding followed by 3, 6 and 9 days of ad libitum feeding, the epididymal white adipose tissue weight increased progressively, reaching the control value at day 9. In contrast, after 8 cycles of starvation-refeeding followed by 9 days of ad libitum feeding, the epididymal white adipose tissue weight did not reach the control value. These results suggest that dieting is associated with body and adipose tissue weight loss as well as with the decrease of plasma triacylglycerol concentration. Furthermore, our results suggest that better maintenance of low adipose tissue weight and low plasma triacylglycerol concentration may be achieved after multiple cycles of starvation-refeeding.

Differential effect of clofibrate on acetyl-CoA carboxylase mRNA level in rat white and brown adipose tissue

Regulation of some lipogenic enzyme gene expression by clofibrate was studied in rat white and brown adipose tissue. In white adipose tissue the drug administration for 14 days to rats resulted in the increase in acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels. Opposing effect of clofibrate on the acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels was found in brown adipose tissue. These data indicate a tissue specificity of clofibrate action on lipogenic enzyme gene expression. The results presented in this paper provide further evidence that hypolipidaemia caused by the treatment with clofibrate cannot be related to the inhibition of fatty acid synthesis in white adipose tissue in rat.

Comparative study of the lipogenic potential of human and rat adipose tissue

The reported low activity of lipogenic enzymes (especially adenosine triphosphate [ATP]-citrate lyase) in human adipose tissue led to the general conclusion that in humans lipogenesis occurs primarily in the liver. However, recent studies indicate that the liver plays a minor role in de novo lipogenesis and suggest that adipose tissue may be the principal lipogenic human tissue. In an attempt to resolve these contradictions we reinvestigated the lipogenic potential of human adipose tissue and compared with adipose tissue of rats fed a high-fat diet for 2 weeks and fasted overnight before death. These conditions mimic the nutritional state of patients at the moment of tissue sampling. We found that overnight fasting of the rats maintained previously for 12 days on a high-fat diet caused a decrease of ATP-citrate lyase of about 7-fold. Thus, in human adipose tissue, the mean activity of ATP-citrate lyase was approximately 8 times lower than in rats fed a high-fat diet and fasted overnight, and about 50 times lower than in rats maintained on normal laboratory diet. Unlike ATP-citrate lyase, fatty acid synthase (FAS) activity was only slightly lower in human adipose tissue than in rats maintained on a normal laboratory diet. Comparable FAS activity was found when rats were fed a high-fat diet and fasted overnight. The average activities of human adipose tissue acetyl-coenzyme A carboxylase, malic enzyme, and glucose-6-phosphate dehydrogenase were approximately 3-, 4-, and 6-fold lower than in adipose tissue from rats fed a high-fat diet and fasted overnight before tissue sampling, while the activity of 6-phosphogluconate dehydrogenase in humans was higher than in rat adipose tissue. No significant differences in lipogenic enzyme activities were found between male and female and between lean and obese patients. The rate of fatty acid synthesis in intact pieces of human adipose tissue was approximately 5 times lower than in adipose tissue pieces of rats fed a high-fat diet and fasted overnight before tissue samples were taken. The comparison of the lipogenic potential of humans and rats (maintained on the diet to mimic the nutritional state of patients at the time of tissue sampling) suggests that human adipose tissue is an important site of fatty acid synthesis.

Adenine incorporation in human and rat endothelium

Adenine (ADE) reutilisation is an important pathway of adenylate pool regeneration. Data on the rate of this process in different types of cells, its regulation and the importance of species differences is limited. In this study we evaluated adenine incorporation rate and the effect of metabolic factors on this process in human and rat endothelium and compared it to adenine phosphoribosyltransferase (APRT) activity. Microvascular endothelial cells from human (HE) and rat (RE) hearts and a transformed human microvascular endothelial cell line (HMEC-1) were investigated. The rate of adenine incorporation into the adenine nucleotide pool under control conditions was 3.1+/-0.3, 82.8+/-11.1 and 115.1+/-11.2 pmol/min per mg protein for HE, RE and HMEC-1, respectively. In the presence of 2.5 mM ribose or elevated inorganic phosphate concentration in the medium (4.8 mM), few changes were observed in all types of cells. In the presence of both ribose and high inorganic phosphate, the rate of adenine incorporation for RE and HMEC-1 was not significantly different from control, while in HE the rate of adenine incorporation into adenine nucleotides was increased by 75%. Activities of APRT in RE and HMEC-1 were 237.7+/-23.2 and 262.0+/-30.6 pmol/min per mg protein respectively while the activity in HE was markedly lower 48.7+/-3.0 pmol/min per mg protein. In conclusion, nucleotide synthesis from adenine seems to be a slow process in human cardiac microvascular endothelium but it is fast and efficient in rat heart microvascular endothelial cells. Low APRT activity in normal human endothelial cells seems to be the most likely mechanism for this. However, adenine incorporation rate and APRT activity could be greatly enhanced in human endothelium, as demonstrated in transformed cells.

Effect of clofibrate on malic enzyme and leptin mRNAs level in rat brown and white adipose tissue

Two previous studies have reported contradictory results regarding the effect of fibrates treatment on obese (ob) gene expression in rodents. The purpose of the present study was to reinvestigate this issue. We examined the effect of clofibrate (fibrate derivative) administration for 14 days to rats on malic enzyme (as an adequate control of fibrates action) and leptin mRNAs level in the white and brown adipose tissues (WAT and BAT, respectively). The malic enzyme activity and malic enzyme mRNA level in white adipose tissue increased significantly after clofibrate feeding. In brown adipose tissue, the drug treatment resulted in depression of malic enzyme activity and malic enzyme mRNA level. Under the same conditions, leptin mRNA level did not change in these tissues. The results presented in this paper provide further evidence that the clofibrate (activator of peroxisome proliferator activated receptor alpha), feeding is without effect on ob gene expression in rat white and brown adipose tissue. Furthermore, the present study demonstrates that clofibrate causes opposite effects on malic enzyme gene expression in WAT (up-regulation) and BAT (down-regulation).

Tissue-specific effect of clofibrate on rat lipogenic enzyme gene expression

Fibrate derivatives are commonly used to treat hyperlipidaemia; however, the mechanism of the antilipidaemic action of these drugs is still unknown. The effect of clofibrate (fibrate derivative) administration for 14 days on lipogenesis and on malic enzyme (EC 1.1.1.40) and fatty acid synthase (EC 2.3.1.85) gene expression in brown and white adipose tissues and in the liver was examined in rats. The rate of brown adipose tissue lipogenesis in the clofibrate-treated animals was significantly lower than that of the control rats. The rate of liver and white adipose tissue lipogenesis was not affected significantly by clofibrate. In brown adipose tissue, the drug treatment resulted in a depression of fatty acid synthase and malic enzyme mRNA levels. The fatty acid synthase mRNA level did not change significantly in the liver, whereas the malic enzyme mRNA level increased approximately 6-fold in this organ after clofibrate treatment. The malic enzyme mRNA level in white adipose tissue increased about 2-fold, while the fatty acid synthase mRNA level was unchanged after clofibrate feeding. The results presented in this paper provide further evidence that the hypolipidaemia caused by treatment of rats with clofibrate cannot be related to the inhibition of fatty acid synthesis in the liver and white adipose tissue. These data also indicate that clofibrate exhibits tissue specificity.

Adenine/ribose supply increases adenosine production and protects ATP pool in adenosine kinase-inhibited cardiac cells

The objective of the present study was to establish the optimal combination of inhibitors of adenosine metabolism and nucleotide precursors resulting in long-term increase in endogenous adenosine concentration without adverse metabolic consequences in non-ischemic cardiomyocytes and endothelial cells. Cardiomyocytes and endothelial cells were isolated after collagenase digestion of the rat heart. Freshly isolated cardiac myocytes or cultured endothelial cells were incubated for up to 8 h with no inhibitors or substrates or with various combinations of adenosine deaminase inhibitor: 5 micron M erythro-9(2-hydroxy-3-nonyl)adenine (EHNA), adenosine kinase inhibitors: 10 micro M 5'-iodotubercidin (ITu) or 10 micro M 5'-aminoadenosine (AA) and nucleotide precursors: 100 micro M adenine, 2.5 mm ribose and 5 mm inorganic phosphate. Nucleotide, nucleoside and base concentrations were evaluated at the end of the incubation by HPLC in cardiomyocyte or endothelial cells extracts and in incubation media. Adenosine content in cardiomyocyte suspension was enhanced after 3 h incubation in the presence of ITu+EHNA as compared to EHNA alone (2.8+/-0.2 v 0.9+/-0.2 nmol/mg protein, respectively). ATP decreased from an initial value of 22.7+/-0.7 nmol/mg protein to 18.9+/-0.7 in the presence of ITu+EHNA, while ATP was maintained at 21.8+/-0.7 nmol/mg protein with EHNA. With adenine+ITu+EHNA, the changes were similar to those observed with ITu+EHNA. However, with ribose+adenine+ITu+EHNA, ATP increased to 25. 8+/-1.2 nmol/mg protein and adenosine concentration was elevated to 3.9+/-0.3 nmol/mg protein. Similar results were observed if AA was used instead of ITu to inhibit adenosine kinase. All the changes were maintained after 8 h of incubation. Adenosine content was increased in endothelial cells incubated with ITu+EHNA to 3.1+/-0.4 nmol/mg protein as compared to 1.1+/-0.2 nmol/mg protein with EHNA alone after 3 h, while ATP decreased (18.1+/-1.1 v 22.0+/-1.4 nmol/mg protein with EHNA+ITu or EHNA, respectively). In the presence of adenine+ITu+EHNA, adenosine content increased after 3 h to 6.5+/-0.9 nmol/mg protein while ATP was elevated to 26.1+/-0.8 nmol/mg protein. Additional presence of ribose was without effect. No changes in adenylate energy charge were observed in cardiomyocytes or endothelium under any conditions studied. Inhibition of adenosine kinase and adenosine deaminase caused a decrease in ATP together with increased adenosine content both in endothelial cells and cardiomyocytes. However, the addition of adenine (endothelial cells) or adenine with ribose (cardiomyocytes) together with inhibitors of adenosine metabolism protected cells from ATP depletion and further increased adenosine concentration.

Dietary alpha-tocopherol prevents dehydroepiandrosterone-induced lipid peroxidation in rat liver microsomes and mitochondria

Dehydroepiandrosterone (DHEA), an adrenal steroid, causes lipid peroxidation in rat liver microsomes and mitochondria and induces hepatocarcinogenesis. It was investigated whether alpha-tocopherol, a naturally occurring free radical chain terminator, could decrease lipid peroxidation. When DHEA-free diet supplemented with increasing concentrations of alpha-tocopherol (25, 50, 100, 200, 400 and 1000 mg/kg diet) was fed to rats for 7 days, a marked lipid peroxidation (measured as thiobarbituric acid reactive substances formation) was observed at concentrations 25 and 50 mg/kg in liver microsomes and mitochondria isolated from these animals. Lipid peroxidation was significantly reduced at concentrations > or = 100 mg/kg. When DHEA (500 mg/kg diet) was fed to rats simultaneously with increasing concentrations of alpha-tocopherol, strong lipid peroxidation was observed at alpha-tocopherol concentrations < or = 200 mg/kg diet. However, microsomes and mitochondria isolated from livers of rats fed alpha-tocopherol at doses of 400 and 1000 mg/kg diet produced only negligible amounts of thiobarbituric acid reactive substances. The data show that high concentrations of alpha-tocopherol in the diet decrease DHEA-induced microsomal and mitochondrial lipid peroxidation. Our results support the concept that alpha-tocopherol can protect against DHEA-induced lipid peroxidation and consequently against steroid-induced liver cell damage and, perhaps, also tumour development.

Unususal increase of lipogenesis in rat white adipose tissue after multiple cycles of starvation-refeeding

The purpose of the study was to determine the response of liver and brown (BAT) and white (WAT) adipose tissue lipogenesis and total body weight in rats subjected to multiple cycles of 3 days of fasting and 3 days of refeeding. Rats fasted for 3 days showed significant reduction in body weight. These changes were reversed on 3 days' refeeding. Body weight was much higher in rats fed ad libitum than in animals experiencing more than one cycle of 3 days of fasting followed by 3 days of refeeding. Despite the significant body weight reduction, an unusual increase of lipogenesis in WAT was found after multiple cycles of starvation-refeeding of rats on standard laboratory diet. The rate of lipogenesis in the liver and BAT was also elevated but to a much smaller extent. A parallel increase in enzymatic activities related to fatty acid synthesis, ie, fatty acid synthase, acetyl-coenzyme A carboxylase, adenosine triphosphate (ATP)-citrate lyase, NADP-linked malic enzyme, and hexose monophosphate shunt dehydrogenases, suggests that the increased rate of lipogenesis in WAT is a consequence of increased lipogenic enzyme activities. These data suggest that upregulation of WAT lipogenesis occurs after the multiple cycles of the starvation-refeeding protocol. An unusual increase of lipogenesis in rat WAT may have a survival advantage, because starved-refed rats must develop the ability to ingest large amounts of food during a refeeding period to store it in a convenient form than can be used as an oxidizable substrate during a period of starvation. Moreover, these results suggest that it is possible to develop appropriate starvation-refeeding conditions that may inhibit body weight gain.

Structural properties and thermal stability of human liver and heart fatty acid binding proteins: a Fourier transform IR spectroscopy study

The secondary structure and the thermal stability of human liver (L-FABP) and heart (H-FABP) fatty acid-binding proteins were analyzed, in the absence and in the presence of oleic acid, by Fourier transform ir spectroscopy. The study was done in order to gain information on the secondary as well three-dimensional structure of L-FABP and to check the possible H-FABP self-association that has been found to occur in rat and pig H-FABP. Comparison of human L-FABP and H-FABP ir spectra reveals that, in spite of the low sequence homology, the two proteins have similar secondary and probably tertiary structures. The ir data indicates that a larger amount of beta-strands are exposed to the solvent in H-FABP as compared to L-FABP, suggesting minor differences in the three-dimensional structures of these proteins. The binding of oleic acid to L-FABP and H-FABP stabilizes their structures and does not modify their secondary structure. The ir spectra neither confirm nor exclude self-association of human H-FABP.

Different regulatory properties of the cytosolic and mitochondrial forms of malic enzyme isolated from human brain

The human brain contains a cytosolic and mitochondrial form of NADP(+)-dependent malic enzyme. To investigate their possible metabolic roles we compared the regulatory properties of these two iso-enzymes. The mitochondrial malic enzyme exhibited a sigmoid substrate saturation curve at low malate concentration which was shifted to the right at both higher pH values and in the presence of low concentration of Mn2+ or Mg2+. Succinate or fumarate increased the activity of the mitochondrial malic enzyme at low malate concentration. Both activators shifted the plot of reaction velocity versus malate concentration to the left, and removed sigmoidicity, but the maximum velocity was unaffected. The activation was associated with a decrease in Hill coefficient from 2.3 to 1.1. The human brain cytosolic malic enzyme displayed a hyperbolic substrate saturation kinetics and no sigmoidicity was detected even at high pH and low malate concentrations. Succinate or fumarate exerted no effect on the enzyme activity. Excess of malate inhibited the oxidative decarboxylation catalysed by cytosolic enzyme at pH 7.0 and below. In contrast, decarboxylation catalysed by mitochondrial malic enzyme, was unaffected by the substrate. These results suggest that under in vivo conditions, cytosolic malic enzyme catalyses both oxidative decarboxylation of malate and reductive carboxylation of pyruvate, whereas the role of mitochondrial enzyme is limited to decarboxylation of malate. One may speculate that in vivo the reaction catalysed by cytosolic malic enzyme supplies dicarboxylic acids (anaplerotic function) for the formation of neurotransmitters, while the mitochondrial enzyme regulates the flux rate via Krebs cycle by disposition of the tricarboxylic acid cycle intermediates (cataplerotic function).