Liver Lipogenic Enzymes Research Articles

Investigating the Levels of Liver Lipogenic and Lipolytic Enzymes in Rat with High-Fat Diet and Sucrose Solution Underwent Progressive Resistance Training

Objective: Consuming too much fat or carbohydrates stimulates lipogenesis and excess fat is stored in non-fat tissues, including the liver, and manifests as obesity and fatty liver disease. This study aimed to investigate the effect of eight weeks of progressive resistance training (PRT) on the liver levels of some enzymes affecting lipid metabolism in rats fed a high-fat diet and sucrose solution.
 Materials and Methods: Twenty-four male wistar rats with 5 weeks of age were randomly divided into two groups: standard diet (SD) (n=8) and high-fat diet and sucrose solution (HFDS) (n=16). Twelve weeks later, HFDS group was divided into two groups: sedentary (HS) and PRT (HPRT). The PRT program was implemented 3 days a week for 8 weeks. Gene expression of AMPKα1, SCD-1, ATGL and FASN enzymes affecting lipid metabolism in liver tissue and its fat content were investigated.
 Results: HFDS significantly increased the body weight (P: 0.001) and significantly decreased the liver expression of ATGL and FASN (P: 0.001, P: 0.011). Eight weeks of PRT did not show a significant difference in the expression of AMPKα1, SCD-1, ATGL and FASN genes. Rats fed HFDS had considerably higher levels of triglyceride (TG) and total cholesterol (TC) in their liver tissue (P: 0.004, P: 0.001) and PRT did not affect them (P: 0.959, P: 0.809 respectively).
 Conclusion: It seems that eight weeks of PRT will not change liver lipid metabolism enzymes. Therefore, modifying the diet and changing it, will probably show different results after PRT.

Hepatic mTORC2 compensates for loss of adipose mTORC2 in mediating energy storage and glucose homeostasis.

Mammalian target of rapamycin complex 2 (mTORC2) is a protein kinase complex that plays an important role in energy homeostasis. Loss of adipose mTORC2 reduces lipogenic enzyme expression and de novo lipogenesis in adipose tissue. Adipose-specific mTORC2 knockout mice also display triglyceride accumulation in the liver. However, the mechanism and physiological role of hepatic triglyceride accumulation upon loss of adipose mTORC2 are unknown. Here, we show that loss of adipose mTORC2 increases the expression of de novo lipogenic enzymes in the liver, thereby causing accumulation of hepatic triglyceride and hypertriglyceridemia. Simultaneous inhibition of lipogenic enzymes in adipose tissue and liver by ablating mTORC2 in both tissues prevented accumulation of hepatic triglycerides and hypertriglyceridemia. However, loss of adipose and hepatic mTORC2 caused severe insulin resistance and glucose intolerance. Thus our findings suggest that increased hepatic lipogenesis is a compensatory mechanism to cope with loss of lipogenesis in adipose tissue, and further suggest that mTORC2 in adipose tissue and liver plays a crucial role in maintaining whole body energy homeostasis.NEW & NOTEWORTHY Loss of adipose and hepatic mTORC2 causes diabetes.

Real-ambient exposure to air pollution exaggerates excessive growth of adipose tissue modulated by Nrf2 signal

Air pollution was becoming a global threat to the public health, which was primarily mediated by PM2.5 induced cardiovascular diseases and pulmonary diseases. Recently, observational epidemiologic studies proposed the link between PM2.5 and obesity. Consistently, the link was also supported by limited animal researches. However, the potential mechanism mediating the harmful effects of PM2.5 was still elusive. In this study, we applied the “real-ambient exposure” system to conduct the experiments, which was closer to the status of ambient air pollution compared with the method of intratracheal instillation and concentrated air particles (CAPs) exposure system. Nuclear factor E2-related factor 2 (Nrf2) was previously reported to protect against inflammation and oxidative stress when exposed to PM2.5. Here, we reported that Nrf2−/− mice developed overgrowth of adipose tissue after “real-ambient exposure” to PM2.5, compared to filtered air (FA) group. Consistently, compared to FA group, adipocytes from subcutaneous (sWAT) and gonadal (gWAT) white adipose tissue of Nrf2−/− mice exhibited enlarged cell size in PM2.5 exposure group. Furthermore, the levels of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) in serum and liver of Nrf2−/− mice were also altered statistically in PM2.5 exposure group. Importantly, when the expression of lipogenic enzymes was analyzed, the levels of the related specific genes in adipose tissue and liver of Nrf2−/− mice were altered in PM2.5 exposure group. Interestingly, the key transcription factors modulating expression of lipogenic enzymes in liver of Nrf2−/− mice were also found altered in PM2.5 exposure group, such as peroxisome proliferator-activated receptor (PPARα, PPARγ). Taken together, our study mimicked the status of ambient air pollution, revealed new insights into the adverse effect of PM2.5 exposure, provided new link between air pollution and overgrowth of adipose tissue, and supported the vital role of Nrf2 in mediating the side effects of PM2.5.

Lack of monoacylglycerol lipase prevents hepatic steatosis by favoring lipid storage in adipose tissue and intestinal malabsorption

Monoacylglycerol lipase (MGL) is the rate-limiting enzyme in the degradation of monoacylglycerols. To examine the role of MGL in hepatic steatosis, WT and MGL KO (MGL-/-) mice were challenged with a Western diet (WD) over 12 weeks. Lipid metabolism, inflammation, and fibrosis were assessed by serum biochemistry, histology, and gene-expression profiling of liver and adipose depots. Intestinal fat absorption was measured by gas chromatography. Primary adipocyte and 3T3-L1 cells were analyzed by flow cytometry and Western blot. Human hepatocytes were treated with MGL inhibitor JZL184. The absence of MGL protected mice from hepatic steatosis by repressing key lipogenic enzymes in liver (Srebp1c, Pparγ2, and diacylglycerol O-acyltransferase 1), while promoting FA oxidation. Liver inflammation was diminished in MGL-/- mice fed a WD, as evidenced by diminished epidermal growth factor-like module-containing mucin-like hormone receptor-like 1 (F4/80) staining and C-C motif chemokine ligand 2 gene expression, whereas fibrosis remained unchanged. Absence of MGL promoted fat storage in gonadal white adipose tissue (gWAT) with increased lipogenesis and unchanged lipolysis, diminished inflammation in gWAT, and subcutaneous AT. Intestinal fat malabsorption prevented ectopic lipid accumulation in livers of MGL-/- mice fed a WD. In vitro experiments demonstrated increased adipocyte size/lipid content driven by PPARγ. In conclusion, our data uncover that MGL deletion improves some aspects of nonalcoholic fatty liver disease by promoting lipid storage in gWAT and fat malabsorption.

Hypoglycemic effect of poly-herbal combination in streptozotocin-induced diabetic rats

<p class="Abstract">The present study evaluates the combinatorial effect of a poly-herbal combination with multiple therapeutic effects as a hypoglycemic and hypolipidemic agent. Herbal combination of <em>Salacia oblonga, Tinospora cordifolia, Emblica officinalis, Curcuma longa</em> and <em>Gymnema sylvestre</em> was prepared and administered to streptozotocin (55 mg/kg, i.p.)-induced diabetic rats, at a dose of 100 mg/kg, for four weeks. The poly-herbal combination significantly elevated the plasma insulin (90%) and reduced serum glucose (42%), cholesterol (49%), triglycerides (43%), LDL cholesterol (62.5%) and plasma apo B/apo A in the diabetic rats. The liver lipogenic enzymes like HMG CoA reductase and glucose-6-phosphatase significantly declined (p<0.05) in their activity while glucose-6-phosphate dehydrogenase and malic enzymes showed higher activity compared to the diabetic control. The results suggest a significant hypoglycemic and hypolipidemic property for the poly-herbal combination.</p><p> </p>

Single administration of recombinant IL-6 restores the gene expression of lipogenic enzymes in liver of fasting IL-6-deficient mice.

Lipogenesis is intimately controlled by hormones and cytokines as well as nutritional conditions. IL-6 participates in the regulation of fatty acid metabolism in the liver. We investigated the role of IL-6 in mediating fasting/re-feeding changes in the expression of hepatic lipogenic enzymes. Gene and protein expression of lipogenic enzymes were examined in livers of wild-type (WT) and IL-6-deficient (IL-6(-/-) ) mice during fasting and re-feeding conditions. Effects of exogenous IL-6 administration on gene expression of these enzymes were evaluated in vivo. The involvement of STAT3 in mediating these IL-6 responses was investigated by using siRNA in human HepG2 cells. During feeding, the up-regulation in the hepatic expression of lipogenic genes presented similar time kinetics in WT and IL-6(-/-) mice. During fasting, expression of lipogenic genes decreased gradually over time in both strains, although the initial drop was more marked in IL-6(-/-) mice. Protein levels of hepatic lipogenic enzymes were lower in IL-6(-/-) than in WT mice at the end of the fasting period. In WT, circulating IL-6 levels paralleled gene expression of hepatic lipogenic enzymes. IL-6 administration in vivo and in vitro showed that IL-6-mediated signalling was associated with the up-regulation of hepatic lipogenic enzyme genes. Moreover, silencing STAT3 in HepG2 cells attenuated IL-6 mediated up-regulation of lipogenic gene transcription levels. IL-6 sustains levels of hepatic lipogenic enzymes during fasting through activation of STAT3. Our findings indicate that clinical use of STAT3-associated signalling cytokines, particularly against steatosis, should be undertaken with caution.

Migratory preparation associated alterations in pectoralis muscle biochemistry and proteome in Palearctic–Indian emberizid migratory finch, red-headed bunting, Emberiza bruniceps

Avian migration is an exceptionally high-energy-demanding process, which is met by the accumulation and utilization of fuel stores as well as the alterations in muscle physiology prior to their flight. Pre-migratory fattening coupled with changes in flight muscle metabolic enzymes and proteome is required to provide the necessary fuel and muscle performance required for migration. We studied how the serum metabolites (urea, uric acid, and creatinine), pectoralis muscle metabolites (glycogen, glucose, and cholesterol), muscle metabolic enzymes (CPT, HOAD, CS, MDH, CCO, CK, LDH, PFK, MLPL, and PK), liver lipogenic enzyme (FAS), and pectoralis muscle proteins get altered in pre-migratory and non-migratory buntings. Significantly increased pectoralis muscle fatty acid oxidation (CPT and HOAD activity), aerobic/anaerobic capacity (CS, CCO, and MDH activity), glycolytic capacity (PFK and PK activity), lipolysis (muscle LPL), and burst power (CK activity) were observed prior to the spring migration in pre-migratory buntings, whereas significantly increased pectoralis muscle anaerobic capacity (LDH activity) was observed in non-migratory buntings. Significant increase in the liver FAS showed profound lipogenesis prior to the spring migration. In this study, we have also investigated whether muscle has differential protein content during the pre-migratory and non-migratory phases of the annual migratory cycle. Twenty-nine proteins are identified and well characterized varying in expression significantly during the pre-migratory and non-migratory phases.These findings indicate that significant pre-migratory fattening and alterations in flight (pectoralis) muscle biochemistry and proteome in between the non- and pre-migratory phases may play a significant role in pre-migratory flight muscle preparation in these long-route migrants.

Liver X receptors connect nuclear O-GlcNAc signaling to hepatic glucose utilization and lipogenesis

Insulin is a central regulator of glycolysis and de novo lipogenesis in the liver. However, hepatic glucose metabolism has been shown to activate the transcription of glycolytic and lipogenenic enzymes independently of insulin. The nuclear liver X receptors LXRa and LXRb play a major role in glucose and lipid metabolism, regulating transcription of glycolytic and lipogenic enzymes in liver, which is believed to be mediated by oxysterol ligand activation and insulin signaling. The majority of hepatic glucose-responsive genes are regulated by carbohydrate response element-binding protein (ChREBP), a transcriptional regulator that requires glucose metabolism via the hexosamine biosynthetic pathway and O-GlcNAc transferase (OGT)-mediated O-GlcNAc modification for full activation. We have previously shown that also LXRs are targets for O-GlcNAc modification in response to glucose and refeeding, promoting lipogenic gene expression. We recently addressed the relative roles of insulin, glucose and LXR in regulating hepatic glycolytic and lipogenic gene expression in vivo by subjecting untreated control and streptozotocin (STZ)-treated LXRa/b +/+ and LXRa/b -/- mice to a fasting-refeeding regime. STZ was used to destroy pancreatic β-cells and insulin production. We found that under hyperglycemic and hypoinsulinemic conditions, LXRs maintained their ability to upregulate the expression of glycolytic and lipogenic enzymes, including glucokinase (GK), sterol regulatory element-binding protein (SREBP-1c), ChREBPa and the newly identified shorter isoform ChREBPb. ChREBPa expression became dependent on LXR under hyperglycemic and hypoinsulinemic conditions, which was mediated, at least in part, by OGT signaling. Moreover, we found that LXR and OGT interacted and co-localized in the nucleus in Huh7 cells and that loss of LXRs profoundly reduced nuclear O-GlcNAc signaling, ChREBP O-GlcNAcylation and activity in vivo . We propose that LXR regulation of nuclear O-GlcNAc signaling and ChREBP O-GlcNAcylation is part of a mechanism linking hepatic glucose utilization with lipid synthesis.

The Potential Benefits and Adverse Effects of Phytic Acid Supplement in Streptozotocin-Induced Diabetic Rats

In this study, the effect of phytic acid supplement on streptozotocin-induced diabetic rats was investigated. Diabetic rats were fed rodent chow with or without phytic acid supplementation for thirty days. Blood and organ samples were collected for assays. The average food intake was the highest and the body weight gain was the lowest in the group fed phytic acid supplement compared to the diabetic and normal control groups. There was a downward trend in intestinal amylase activity in the group fed phytic acid supplement compared to the other groups. The spike in random blood glucose was the lowest in the same group. We noted reduced serum triglycerides and increased total cholesterol and HDL cholesterol levels in the group fed phytic acid supplement. Serum alkaline phosphatase and alanine amino transferase activities were significantly (P < 0.05) increased by phytic acid supplementation. Systemic IL-1β level was significantly (P < 0.05) elevated in the diabetic control and supplement treated groups. The liver lipogenic enzyme activities were not significantly altered among the groups. These results suggest that phytic acid supplementation may be beneficial in the management of diabetes mellitus. The observed adverse effect on the liver may be due to the combined effect of streptozotocin-induced diabetes and phytic acid supplementation.

Effect of long term feeding with conjugated linoleic acid (CLA) in growth performance and lipid metabolism of European sea bass (Dicentrarchus labrax)

In the present study, the effects of long term feeding dietary conjugated linoleic acid (CLA) on growth, liver and perivisceral fat morphology, lipid metabolism enzymes and prostaglandin production potential were assessed. Two hundred and forty-three European sea bass (152.4±1.96g) were randomly allocated in 9 indoor 1m3 fiberglass tanks (4.1kg/m3) and assigned three diets containing graded amounts of CLA (0, 0.5 and 1%) for 20weeks. Dietary CLA did not affect growth performance or tissue proximate composition although increased the saturated fatty acid fraction in fish fed with 1% CLA in muscle. Muscle and liver fatty acid profiles were slightly altered by CLA inclusion, mainly by the increase of the CLA isomers and by the increase of 18:0 and the decrease of 16:1n-7. Liver lipogenic and lipolytic enzymes were not affected by dietary CLA. Hepatocyte area was reduced in fish fed with 1% of CLA, as well as adipocyte area in fish fed with 0.5% of CLA where adipocyte number by unit of area also increased. Head kidney prostaglandins' production potential was reduced in fish fed with 1% of CLA, having also a negative correlation with dietary CLA level of inclusion. The present results suggest that CLA can be incorporated up to 1% in 150g European sea bass for 20weeks without affecting fish performance or enzyme activities and at the time improves liver and adipose tissue morphology.

Dietary leucine and alanine supplementation have similar effects in the prevention of high fat diet induced obesity

High protein diets can alleviate detrimental effects of high fat diets as discussed to be partially due to Leu. C57BL/6 male mice were fed ad libitum for 1 wk with high‐fat diets (20% of fat) containing an adequate (10%, APD) or high (50%, HPD) amount of whey protein, or supplemented with Leu corresponding to the Leu content within the HP diet (LD) or supplemented equimolar with Ala (AD) in order to clarify the specificity of Leu effects. Food and water intake were monitored (computer controlled system). Body composition was assessed (QMR). HP completely prevented the AP induced accumulation of body fat. LD and AD resulted in similar reductions of body fat accumulation which was intermediate between AP and HP. Triacylglycerol concentrations and gene expression of lipogenic enzymes in liver as well as plasma cholesterol were lower by HP compared to AP, both LD and AD showed intermediate effects. Body fat gains correlated with total energy intake (P&lt;0.0001). Water intake rapidly increased by HP feeding and correlated with total nitrogen intake (P&lt;0.0001). Feed energy efficiency correlated with energy intake (P&lt;0.0001). We concluded that the positive effects of high protein diets on metabolic syndrome associated traits are mainly due to effects on satiety linked to amino‐N intake. There is no specific metabolic effect of Leu at least in the short term. Grants PE643/7‐1, PE643/10‐1, Deutsche Forschungsgemeinschaft, Germany.

The HPA axis modulates the CNS melanocortin control of liver triacylglyceride metabolism

The central melanocortin system regulates lipid metabolism in peripheral tissues such as white adipose tissue. Alterations in the activity of sympathetic nerves connecting hypothalamic cells expressing melanocortin 3/4 receptors (MC3/4R) with white adipocytes have been shown to partly mediate these effects. Interestingly, hypothalamic neurons producing corticotropin-releasing hormone and thyrotropin-releasing hormone co-express MC4R. Therefore we hypothesized that regulation of hypothalamo-pituitary adrenal (HPA) and hypothalamo-pituitary thyroid (HPT) axes activity by the central melanocortin system could contribute to its control of peripheral lipid metabolism. To test this hypothesis, we chronically infused rats intracerebroventricularly (i.c.v.) either with an MC3/4R antagonist (SHU9119), an MC3/4R agonist (MTII) or saline. Rats had been previously adrenalectomized (ADX) and supplemented daily with 1mg/kg corticosterone (s.c.), thyroidectomized (TDX) and supplemented daily with 10μg/kgL-thyroxin (s.c.), or sham operated (SO). Blockade of MC3/4R signaling with SHU9119 increased food intake and body mass, irrespective of gland surgery. The increase in body mass was accompanied by higher epididymal white adipose tissue (eWAT) weight and higher mRNA content of lipogenic enzymes in eWAT. SHU9119 infusion increased triglyceride content in the liver of SO and TDX rats, but not in those of ADX rats. Concomitantly, mRNA expression of lipogenic enzymes in liver was increased in SO and TDX, but not in ADX rats. We conclude that the HPA and HPT axes do not play an essential role in mediating central melanocortinergic effects on white adipose tissue and liver lipid metabolism. However, while basal hepatic lipid metabolism does not depend on a functional HPA axis, the induction of hepatic lipogenesis due to central melanocortin system blockade does require a functional HPA axis.

Fat digestion and absorption in spice-pretreated rats.

A few common spices are known to stimulate secretion of bile with higher amount of bile acids which play a major role in digestion and absorption of dietary lipids. It would be appropriate to verify if these spices enable efficient digestion and absorption during high-fat intake. In this context, dietary ginger (0.05%), piperine (0.02%), capsaicin (0.015%), and curcumin (0.5%) were examined for their influence on bile secretion, digestive enzymes of pancreas and absorption of dietary fat in high-fat (30%) fed Wistar rats for 8 weeks. These spices enhanced the activity of pancreatic lipase, amylase, trypsin and chymotrypsin by 22-57%, 32-51%, 63-81% and 12-38%, respectively. Dietary intake of spices along with high-fat enhanced fat absorption. These dietary spices increased bile secretion with higher bile acid content. Stimulation of lipid mobilisation from adipose tissue was suggested by the decrease in perirenal adipose tissue weight by dietary capsaicin and piperine. This was also accompanied by prevention of the accumulation of triglyceride in liver and serum in high-fat fed rats. Activities of key lipogenic enzymes in liver were reduced which was accompanied by an increased activity of hormone-sensitive lipase. Thus, dietary ginger and other spice compounds enhance fat digestion and absorption in high-fat fed situation through enhanced secretion of bile salts and a stimulation of the activity pancreatic lipase. At the same time, the energy expenditure is facilitated by these spices to prevent the accumulation of absorbed fat.

Effects of dietary vegetable oils on liver and gonad fatty acid metabolism and gonad maturation in gilthead seabream (Sparus aurata) males and females

A 20-week growth trial was conducted to investigate the effect of two dietary blended vegetable oils (VO) on liver lipogenic enzyme activity, liver and gonad lipid class composition and fatty acid profiles, serum sex hormones, and gonad morphohistology in gilthead seabream, Sparus aurata. Three groups of fish (BWi 130.9 ± 3.1 g) were fed, close to satiation, three experimental diets: a control (CTRL) contained fish oil (FO) as the sole lipid source (100% FO) and two VO-blended diets in each 60% of FO was substituted by an equal mixture of cottonseed oil (CO), sunflower oil (SFO) and either linseed oil (LO) or soybean oil (SBO), designated as LO or SBO diet, respectively. Each diet was assigned to triplicate groups of fish. Results showed that all dietary treatments presented no significant (P > 0.05) differences in growth rate and feed conversion ratio for sexes combined. Enzyme activities of liver lipogenic enzymes of LO-fed fish (glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME) and fatty acid synthetase (FAS)) were not statistically (P > 0.05) different from those of CTRL fish. Only in the group of fish fed the SBO diet, G6PDH was slightly higher (P < 0.05) for both sexes, while ME showed a significant (P < 0.05) higher activity only in females relative to CTRL fish. Liver FAS enzyme activity remained unaltered among dietary groups. VO-fed fish recorded a significant (P < 0.05) increase in total lipid (TL) and triglyceride (TAG) contents in both liver and gonad, more pronounced in females than in males, concurrent with a significant (P < 0.05) decrease in cholesterol (CHL) and phospholipids (PL), more obvious for the SBO-fed fish, as compared to CTRL. The fatty acid (FA) composition of liver or gonad reflected that of the supplied diet and evidenced a significant (P < 0.01 or <0.05) alteration in the majority of individual FA in VO-fed fish compared to CTRL. There were decreased levels of ARA (20:4 n-6), EPA (20:5 n-3), and DHA (22:6 n-3) in VO-fed fish, more pronounced in females than in males, compared to CTRL. The liver and gonad FA profiles, for males and females, reflected the composition of the diet and showed sex variation in the output of multivariate principal component analysis (PCA). Feeding fish VO diets has also led to a significant (P < 0.05) reduction in serum estradiol level by 15.8 or 22.3% in LO- or SBO-fed fish, respectively, and in testosterone level by 7.7% in the latter dietary group only compared to the CTRL. Histomorphological examination of ovary and testis has indicated a relative retardation in oogenesis and spermatogenesis in VO-fed fish, less obvious in the LO-fed fish compared to CTRL. These results suggest a preference of LO over SBO blend diet in terms of liver lipogenic enzyme activity, liver and gonad lipid content, lipid class composition and fatty acid profile, serum sex hormones as well as gonad maturation. PCA analysis of gonads highlighted the importance of using a 100% marine FO diet for gilthead seabream broodstock for the recovery of a normal FA profile in gonads of fish, previously fed VO over the production cycle, to ensure successful spawning.

Chinese prescription Kangen-karyu prevents dyslipidaemia and oxidative stress in mouse model of type 2 diabetes

We have investigated the effects of Kangen-karyu, a Chinese prescription, on the lipid metabolism and oxidative stress in a type 2 diabetes model. Male db/db mice were divided into three groups: control (vehicle), Kangen-karyu 100 or 200 mg/kg body weight/day orally administered mice. Age-matched non-diabetic m/m mice were used as a normal group. The administration of Kangen-karyu reduced hyperglycaemia and hyperlipidaemia in db/db type 2 diabetic mice through a decline in the serum levels of glucose and lipids, and an improvement of lipoprotein profiles. The increased oxidative stress in db/db mice was attenuated by the administration of Kangen-karyu through inhibiting the generation of reactive oxygen species and lipid peroxidation. The enhanced hepatic triglyceride and total cholesterol levels of the db/db mice were significantly reduced by Kangen-karyu administration through down-regulation of sterol regulatory element-binding protein-1 and lipogenic enzymes in liver. Furthermore, the expressions of hepatic nuclear factor-kappa B (NF-κB) and cyclooxygenase-2 and inducible nitric oxide synthase protein levels were also augmented in db/db mice. However, Kangen-karyu reduced the expressions of these inflammatory proteins by inhibiting NF-κB activation in db/db type 2 diabetes. This study suggests that Kangen-karyu may improve oxidative stress via the regulation of dyslipidaemia in type 2 diabetes.

Effect of Andrographolide and Ethanol Extract of Andrographis paniculata on Liver Glycolytic, Gluconeogenic, and Lipogenic Enzymes in a Type 2 Diabetic Rat Model

Andrographis paniculata (Burm.f.) Nees (Acanthaceae) (AP), containing the major active principle, andrographolide,(AG) has been used ethnomedically in the treatment of diabetes and hypertension in Malaysia and India. Type 2 diabetes mellitus was induced by administering nicotinamide (NA) 180 mg/kg i.p., followed by streptozotocin (STZ) 45 mg/kg i.p., 15 min later and allowed for 15 days to develop. Diabetic rats treated with active principle andrographolide 10 mg/kg and ethanol extract of Andrographis paniculata at doses of 500 and 1000 mg/kg, p.o, for 21 days, caused a significant reduction in fasting serum glucose levels on all days analysed (P < 0.01). Treatment with andrographolide and extract showed an increase in glucokinase (GK; P < 0.05), hexokinase (HK; P < 0.05), and lactate dehydrogenase (LDH; P < 0.05) enzyme levels respectively. Significant reductions were observed in serum cholesterol (P < 0.05), triglycerides (P < 0.05), free fatty acids (P < 0.05), and liver glucose 6-phosphatase (G6P’Tase; P < 0.05) enzyme levels on treatment with andrographolide and extract. Glucose 6-phosphate dehydrogenase (G6PDH; P < 0.05) level also showed a significant increase on treatment with andrographolide and extract. Liver antioxidant status (P < 0.05) also improved significantly on treatment with andrographolide and extract. However, no significant increase in serum insulin was found on treatment with either andrographolide or extract, suggesting an effective extra pancreatic mechanism. Thus, the present study demonstrates that andrographolide at 10 mg/kg, and ethanol extract of Andrographis paniculata at 500 and 1000 mg/kg, p.o., on treatment for 21 days, exhibited antidiabetic, hypolipidemic, and antioxidant activities in an adult streptozotocin-nicotinamide type 2 diabetes mellitus model. The results support the traditional use of Andrographis paniculata in the treatment of type 2 diabetes mellitus, and its associated plethora of complications.

Pharmacological Doses of Triiodothyronine Upregulate Lipogenic Enzyme Gene Expression in Rat White Adipose Tissue

Triiodothyronine (T (3)) is known to increase liver lipogenic enzyme gene expression both in vivo and in tissue culture. Conflicting results have been reported on the effect of T (3) on lipogenic enzyme gene expression in white adipose tissue. The results presented in this paper indicate that administration of pharmacological doses of T (3) in rats leads to increased fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), ATP-citrate lyase (ACL) and malic enzyme (ME) activity in white adipose tissue. The increase in lipogenic enzyme activity was associated with increased FAS, ACC, ACL and ME mRNA levels. The response was dose-dependent. Activity of lipogenic enzyme and the lipogenic enzyme mRNA levels were positively correlated to serum T (3) concentration. The in vivo effect of T (3) on lipogenic enzyme gene expression could be reproduced in primary white rat adipocyte culture. In conclusion, the results presented in this paper indicate that T (3) exerts a stimulatory effect on lipogenic enzyme gene expression in white adipose tissue both in vivo and in tissue culture. Significant effects of T (3) on lipogenic enzyme gene expression were only observed in the presence of relatively high (pharmacological) concentrations of the hormone.

Mechanisms of regulation of gene expression by fatty acids

Fatty acids (FA) regulate the expression of genes involved in lipid and energy metabolism. In particular, two transcription factors, sterol regulatory element binding protein-1c (SREBP-1c) and peroxisome proliferator activated receptor alpha (PPARalpha), have emerged as key mediators of gene regulation by FA. SREBP-1c induces a set of lipogenic enzymes in liver. Polyunsaturated fatty acids (PUFA), but not saturated or monounsaturated FA, suppress the induction of lipogenic genes by inhibiting the expression and processing of SREBP-1c. This unique effect of PUFA suggests that SREBP-1c may regulate the synthesis of unsaturated FA for incorporation into glycerolipids and cholesteryl esters. PPARalpha plays an essential role in metabolic adaptation to fasting by inducing the genes for mitochondrial and peroxisomal FA oxidation as well as those for ketogenesis in mitochondria. FA released from adipose tissue during fasting are considered as ligands of PPARalpha. Dietary PUFA, except for 18:2 n-6, are likely to induce FA oxidation enzymes via PPARalpha as a "feed-forward " mechanism. PPARalpha is also required for regulating the synthesis of highly unsaturated FA, indicating pleiotropic functions of PPARalpha in the regulation of lipid metabolic pathways. It is yet to be determined whether FA regulate other transcription factors such as liver-X receptor, hepatocyte nuclear factor 4, and carbohydrate response element binding protein.

Carbohydrate response element binding protein directly promotes lipogenic enzyme gene transcription

Carbohydrate response element (ChRE)-binding protein (ChREBP) is a recently discovered transcription factor that is activated in response to high glucose concentrations in liver independently of insulin. ChREBP was first identified by its ability to bind the ChRE of the liver pyruvate kinase (LPK) gene. We recently reported that the increase in expression of multiple liver lipogenic enzyme mRNAs elicited by feeding a high-carbohydrate diet as well as that of LPK mRNA is markedly reduced in mice lacking ChREBP gene expression (ChREBP(-/-)) in comparison to WT mice. The present study provides evidence for a direct and dominant role of ChREBP in the glucose regulation of two key liver lipogenic enzymes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). ACC, FAS, and LPK mRNA levels were higher in WT hepatocytes cultured with high (25 mM) rather than low (5.5 mM) glucose medium, but there was no effect of glucose concentration on these mRNA levels in ChREBP(-/-) hepatocytes. Similarly, reporter constructs containing ACC, FAS, or LPK gene ChREs were responsive to glucose when transfected into WT but not ChREBP(-/-) hepatocytes, and glucose transactivation of the constructs in ChREBP(-/-) hepatocytes was restored by cotransfection with a ChREBP expression plasmid. ChREBP binding to ACC, FAS, and LPK ChRE sequences in vitro was demonstrated by electrophoretic mobility super shift assays. In vivo binding of ChREBP to ACC, FAS, and LPK gene promoters in intact liver nuclei from rats fed a high-carbohydrate diet was demonstrated by using a formaldehyde crosslinking and chromatin immunoprecipitation procedure.

The trans-10,cis-12 isomer of conjugated linoleic acid reduces hepatic triacylglycerol content without affecting lipogenic enzymes in hamsters.

Conjugated linoleic acid (CLA) refers to the positional and geometric dienoic isomers of linoleic acid. The dietary intake of CLA has been associated with changes in lipid metabolism. The aim of the present work was to assess the effects of the two main isomers of CLA on sterol regulatory element binding protein (SREBP)-1a and SREBP-1c mRNA levels, as well as on mRNA levels and the activities of several lipogenic enzymes in liver. For this purpose hamsters were fed an atherogenic diet supplemented with 5 g linoleic acid, cis-9,trans-11 or trans-10,cis-12 CLA/kg diet for 6 weeks. The trans-10,cis-12 isomer intake produced significantly greater liver weight, but also significantly decreased liver fat accumulation. No changes in mRNA levels of SREBP-1a, SREBP-1c and lipogenic enzymes, or in the activities of these enzymes, were observed. There was no effect of feeding cis-9,trans-11 CLA. These results suggest that increased fat accumulation in liver does not occur on the basis of liver enlargement produced by feeding the trans-10,cis-12 isomer of CLA in hamsters. The reduction in hepatic triacylglycerol content induced by this isomer was not attributable to changes in lipogenesis.