The actions of a novel lipoprotein lipase activator, NO-1886, in hypertriglyceridemic fructose-fed rats

Identification and Characterization of Variants in Intron 6 of the LPL Gene Locus among a Sample of the Kuwaiti Population

Lipoprotein lipase (LPL) is responsible for the hydrolysis of lipoproteins; hence defective LPL is associated with metabolic disorders. Here, we identify certain intronic insertions and deletions (InDels) and single nucleotide polymorphisms (SNPs) in intron 6 of the LPL gene and investigate their associations with different phenotypic characteristics in a cohort of the general Kuwaiti population. Two specific regions of intron 6 of the LPL gene, which contain InDels, were amplified via Sanger sequencing in 729 subjects. Genotypic and allelic frequencies were estimated, and genetic modeling was used to investigate genetic associations of the identified variants with lipid profile, body mass index (BMI), and risk of coronary heart disease (CHD). A total of 16 variants were identified, including 2 InDels, 2 novel SNPs, and 12 known SNPs. The most common variants observed among the population were rs293, rs274, rs295, and rs294. The rs293 “A” insertion showed a significant positive correlation with elevated LDL levels, while rs295 was significantly associated with increased BMI. The rs274 and rs294 variants showed a protective effect of the minor allele with decreased CHD prevalence. These findings shed light on the possible role of LPL intronic variants on metabolic disorders.

Effects of Excess Energy Intake on Glucose and Lipid Metabolism in C57BL/6 Mice

Excess energy intake correlates with the development of metabolic disorders. However, different energy-dense foods have different effects on metabolism. To compare the effects of a high-fat diet, a high-fructose diet and a combination high-fat/high-fructose diet on glucose and lipid metabolism, male C57BL/6 mice were fed with one of four different diets for 3 months: standard chow; standard diet and access to fructose water; a high fat diet; and a high fat diet with fructose water. After 3 months of feeding, the high-fat and the combined high-fat/high-fructose groups showed significantly increased body weights, accompanied by hyperglycemia and insulin resistance; however, the high-fructose group was not different from the control group. All three energy-dense groups showed significantly higher visceral fat weights, total cholesterol concentrations, and low-density lipoprotein cholesterol concentrations compared with the control group. Assays of basal metabolism showed that the respiratory quotient of the high-fat, the high-fructose, and the high-fat/high-fructose groups decreased compared with the control group. The present study confirmed the deleterious effect of high energy diets on body weight and metabolism, but suggested that the energy efficiency of the high-fructose diet was much lower than that of the high-fat diet. In addition, fructose supplementation did not worsen the detrimental effects of high-fat feeding alone on metabolism in C57BL/6 mice.

Dietary fructose feeding increases adipose methylglyoxal accumulation in rats in association with low expression and activity of glyoxalase-2

Methylglyoxal is a precursor to advanced glycation endproducts that may contribute to diabetes and its cardiovascular-related complications. Methylglyoxal is successively catabolized to d-lactate by glyoxalase-1 and glyoxalase-2. The objective of this study was to determine whether dietary fructose and green tea extract (GTE) differentially regulate methylglyoxal accumulation in liver and adipose, mediated by tissue-specific differences in the glyoxalase system. We fed six week old male Sprague-Dawley rats a low-fructose diet (10% w/w) or a high-fructose diet (60% w/w) containing no GTE or GTE at 0.5% or 1.0% for nine weeks. Fructose-fed rats had higher (P < 0.05) adipose methylglyoxal, but GTE had no effect. Plasma and hepatic methylglyoxal were unaffected by fructose and GTE. Fructose and GTE also had no effect on the expression or activity of glyoxalase-1 and glyoxalase-2 at liver or adipose. Regardless of diet, adipose glyoxalase-2 activity was 10.8-times lower (P < 0.05) than adipose glyoxalase-1 activity and 5.9-times lower than liver glyoxalase-2 activity. Adipose glyoxalase-2 activity was also inversely related to adipose methylglyoxal (r = −0.61; P < 0.05). These findings suggest that fructose-mediated adipose methylglyoxal accumulation is independent of GTE supplementation and that its preferential accumulation in adipose compared to liver is due to low constitutive expression of glyoxalase-2.

Increased magnesium intake prevents hyperlipidemia and insulin resistance and reduces lipid peroxidation in fructose-fed rats

Studies have suggested that type 2 diabetes mellitus is associated with abnormal lipid metabolism, oxidative stress and insulin resistance. Increased magnesium intake may improve dyslipidemia, oxidative stress and insulin insensitivity in type 2 diabetes. Therefore, the present study investigated the influence of increasing dietary magnesium from 0.1% to 1.0% for 4 weeks on plasma lipids, lipid peroxidation, l-ascorbic acid and insulin sensitivity in male Wistar rats fed a high-fructose diet. The rats were divided into control (CR), fructose-fed (FRU-fed) and fructose-fed supplemented with magnesium (FRU-Mg-fed) groups (n=8 per group). Homeostasis model assessment for insulin resistance (HOMA-IR) and plasma thiobarbituric acid-reactive substances (TBARS) were used as indices of insulin sensitivity and lipid peroxidation, respectively. When compared with controls, the FRU-fed group had significantly higher values of HOMA-IR, fasting plasma glucose, insulin, triglyceride, total cholesterol/HDL-cholesterol ratio (atherogenic index), and TBARS. Their values in FRU-Mg-fed group were close to those of the controls. FRU-Mg-fed group had also significantly higher plasma magnesium and l-ascorbic acid levels, but significantly lower LDL-cholesterol levels than those in control and Fru-fed groups.

CONCLUSION

increased magnesium intake improved insulin sensitivity, hyperglycemia, hyperlipidemia and reduced lipid peroxidation in fructose-fed rats.

Effect of Skim Milk and Dahi (Yogurt) on Blood Glucose, Insulin, and Lipid Profile in Rats Fed with High Fructose Diet

In the present study, the effect of skim milk and the fermented milk product named dahi (yogurt) on plasma glucose, insulin, and lipid levels as well as on liver glycogen and lipid contents in rats fed with high fructose diet has been investigated. Rats were fed with high fructose diet (21%) supplemented with skim milk, dahi (10 g/day each), or no milk product (control group) for 6 weeks. After 6 weeks of high fructose diet administration, the plasma glucose became significantly higher in control animals (246 mg/dL), whereas it was lower in skim milk (178 mg/dL)- and dahi (143 mg/dL)-fed rats. The glucose tolerance became impaired at the third week of feeding of high fructose diet in control animals, whereas in skim milk- and dahi-fed animals achievement of glucose intolerance was delayed until the fourth and fifth week, respectively. Blood glycosylated hemoglobin and plasma insulin were significantly lower in skim milk (10% and 34%, respectively)- and dahi (17%, and 48%, respectively)-fed animals than those of the control group. Plasma total cholesterol, triglycerides, low-density lipoprotein-cholesterol, and very-low-density lipoprotein-cholesterol and blood free fatty acids were significantly lower in skim milk (13%, 14%, 14%, 19%, and 14%, respectively)- and dahi (22%, 33%, 30%, 33%, and 29%, respectively)-fed animals as compared with control animals. Moreover, the total cholesterol, triglyceride, and glycogen contents in liver tissues were also lower in skim milk (55%, 50%, and 36%, respectively)- and dahi (64%, 27%, and 4%, respectively)-fed animals as compared with control animals. In contrast, high-density lipoprotein-cholesterol in plasma was higher in skim milk (14%)- and dahi (29%)-fed animals as compared with control animals. These results indicate that skim milk and its fermented milk product, dahi, delay the progression of fructose-induced diabetes and dyslipidemia in rats and that these may be useful as antidiabetic food supplements that can be included in daily meals of the diabetic as well as normal population.

Effects of NO-1886 on inflammation-associated cytokines in high-fat/high-sucrose/high-cholesterol diet-fed miniature pigs

Inflammation, closely associated with obesity, is emerging as an important risk factor for the pathophysiological development of atherosclerosis and diabetes mellitus. Fat balance is critical in the aetiology of obesity. Lipoprotein lipase is an important enzyme in lipid metabolism. The aim of this study was to investigate the long-term effect of the lipoprotein lipase activator, NO-1886, on inflammation cytokines, adiposity and related diseases in miniature pigs fed a high-fat/high-sucrose/high-cholesterol diet (HFSC diet). Chinese Bama-miniature pigs were fed a control diet or HFSC diet with or without NO-1886 for 5 months. The levels of inflammation-associated cytokines were determined using the antibody arrays. Feeding of the HFSC diet to miniature pigs markedly increased the expression of inflammatory cytokines. On the other hand, supplementation of NO-1886 to HFSC diet decreased the expression of inflammatory cytokines significantly, protecting against the development of atherosclerosis and diabetes mellitus. NO-1886 may have a beneficial effect on the most inflammation-associated cytokines, and this effect may contribute to improving atherosclerosis and diabetes mellitus.

NO-1886 (ibrolipim), a lipoprotein lipase-promoting agent, accelerates the expression of UCP3 messenger RNA and ameliorates obesity in ovariectomized rats

The synthetic compound NO-1886 (ibrolipim, [4-(4-bromo-2-cyano-phenylcarbamoyl)-benzyl]-phosphonic acid diethyl ester, CAS 133208-93-2) is a lipoprotein lipase (LPL)-promoting agent that decreases plasma triglycerides, increases high-density lipoprotein cholesterol levels, and prevents fat accumulation in high fat-fed rats. However, the effect of NO-1886 on body weight, fat accumulation, and energy expenditure in ovariectomized (OVX) rats is not clear. The primary aim of this study was to ascertain whether NO-1886 ameliorated obesity in OVX rats and to examine the effects on fatty acid oxidation-related enzymes. NO-1886 decreased accumulation of visceral fat and suppressed the increase in body weight resulting from the ovariectomy. NO-1886 decreased the respiratory quotient and increased expression of the fatty acid translocase messenger RNA (mRNA) in the liver, soleus muscle, and mesenteric fat. NO-1886 also increased the expression of fatty acid-binding protein mRNA in the liver and soleus muscle and the expression of the uncoupling protein 3 (UCP3) mRNA in the heart, soleus muscle, and mesenteric fat, but not in the brown adipose tissue. Furthermore, NO-1886 did not affect UCP1 and UCP2 in brown adipose tissue. Therefore, amelioration of obesity by NO-1886 in OVX rats is possibly because of an the increased expression of fatty acid oxidation-related enzymes and UCP3, both of which are related to fatty acid transfer and fat use. Our study indicates that the LPL-promoting agent NO-1886 may be potentially beneficial in the treatment of obesity and obesity-linked health problems in postmenopausal women.

NO-1886 (ibrolipim), a lipoprotein lipase activator, increases the expression of uncoupling protein 3 in skeletal muscle and suppresses fat accumulation in high-fat diet-induced obesity in rats

Although the lipoprotein lipase (LPL) activator NO-1886 shows antiobesity effects in high-fat-induced obese animals, the mechanism remains unclear. To clarify the mechanism, we studied the effects of NO-1886 on the expression of uncoupling protein (UCP) 1, UCP2, and UCP3 in rats. NO-1886 was mixed with a high-fat chow to supply a dose of 100 mg/kg to 8-month-old male Sprague-Dawley rats. The animals were fed the high-fat chow for 8 weeks. At the end of the administration period, brown adipose tissue (BAT), mesenteric fat, and soleus muscle were collected and levels of UCP1, UCP2, and UCP3 messenger RNA (mRNA) were determined. NO-1886 suppressed the body weight increase seen in the high-fat control group after the 8-week administration (585 +/- 39 vs 657 +/- 66 g, P < .05). NO-1886 also suppressed fat accumulation in visceral (46.9 +/- 10.4 vs 73.7 +/- 14.5 g, P < .01) and subcutaneous (43.1 +/- 18.1 vs 68.9 +/- 18.8 g, P < .05) tissues and increased the levels of plasma total cholesterol and high-density lipoprotein cholesterol in comparison to the high-fat control group. In contrast, NO-1886 decreased the levels of plasma triglycerides, nonesterified free fatty acid, glucose, and insulin. NO-1886 increased LPL activity in soleus muscle (0.082 +/- 0.013 vs 0.061 +/- 0.016 mumol of free fatty acid per minute per gram of tissue, P < .05). NO-1886 increased the expression of UCP3 mRNA in soleus muscle 3.14-fold (P < .01) compared with the high-fat control group without affecting the levels of UCP3 in mesenteric adipose tissue and BAT. In addition, NO-1886 did not affect the expression of UCP1 and UCP2 in BAT, mesenteric adipose tissue, and soleus muscle. In conclusion, NO-1886 increased the expression of UCP3 mRNA and LPL activity only in skeletal muscle. Therefore, a possible mechanism for NO-1886's antiobesity effects in rats may be the enhancement of LPL activity in skeletal muscle and the accompanying increase in UCP3 expression.

FR177391, A New Anti-hyperlipidemic Agent from Serratia

The pharmacological effect of FR177391, isolated from Serratia liquefaciens No. 1821, was studied in normal animals and various types of animal models of hypertriglyceridemia. Treatment of normal mice with FR177391 resulted in an increase in heparin-releasable lipoprotein lipase (LPL) activity in the blood and epididymal fat tissue. FR177391 treatment decreased triglyceride (TG) and increased high-density lipoprotein cholesterol in the blood in normal rats following 7 days treatment, suggesting potent LPL activating properties of FR177391. Both Triton WR1339-induced severe and fructose-induced mild hypertriglyceridemia in rats were attenuated by FR177391 treatment. Severely elevated levels of TG in db/db mice, an insulin resistant diabetic animal model, also significantly decreased from 14 days of treatment with FR177391. FR177391 treatment for 9 days caused a decrease in the elevated levels of TG in mice induced by intraperitoneal inoculation of murine lymphoma EL-4. Overall, this study demonstrated that FR177391 can be possibly a LPL activating agent and that FR177391 treatment improved hypertriglyceridemia in various rat and mouse animal models. These results suggest that FR177391 is a promising candidate compound for the management of hypertriglyceridemia.

Effect of Acanthopanax senticosus on lipoprotein lipase in 3T3-L1 adipocytes

The effect of Acanthopanax senticosus (AS) leaves on lipoprotein lipase (LPL) was investigated in 3T3-L1 adipocytes. A water extract of AS leaves increased the LPL activity in culture medium of adipocytes in a dose- and time-dependent manner. The AS extract contained heparin-like LPL releasing components, however, the increase of medium LPL activity was continued up until 12 h, in contrast to the rapid decline after heparin treatment. The increase of LPL mRNA was also observed after AS extract treatment, suggesting that LPL induction occurs at the transcriptional level. The AS extract could partially reverse the LPL suppression by tumour necrosis factor-alpha in 3T3-L1 adipocytes. These results of an AS extract-induced increase of LPL activity in vitro suggest the possible action of AS as a facilitator of plasma triglyceride clearance.

Lipoprotein lipase activator NO-1886 (ibrolipim) accelerates the mRNA expression of fatty acid oxidation-related enzymes in rat liver

The lipoprotein lipase (LPL) activator NO-1886 (ibrolipim) has been shown to have potential benefits for the treatment of obesity in rats. However, the anti-obesity mechanism of NO-1886 has not been clearly understood. To address this, we studied the effects of NO-1886 on the mRNA expression of fatty acid oxidation-related enzymes in rats. The respiratory quotient (RQ) in rats administered a single oral dose of NO-1886 was significantly lower than control rats under both fed and fasted conditions. NO-1886 orally administered to rats for 7 days caused 1.54-fold increase in carnitine palmitoyl transferase II (CPTII) mRNA in the carnitine palmitoyl transferase system. Furthermore, NO-1886 caused a 1.47-fold increase in long-chain acyl-CoA dehydrogenase (LCAD) mRNA, a 1.49-fold increase in acetyl-CoA acyltransferase 2 (ACAA2) mRNA, and a 1.24-fold increase in enoyl-CoA hydratase (ECH) mRNA in rats, all which are liver beta-oxidation enzymes. NO-1886 also increased uncoupling protein-2 (UCP2) mRNA levels in liver by 1.42-fold when compared to the control group. These results suggest that the LPL activator NO-1886 may accelerate the expression of fatty acid oxidation-related enzymes, resulting in a reduction of RQ.

Oligofructose protects against the hypertriglyceridemic and pro-oxidative effects of a high fructose diet in rats

Recent findings indicate that in addition to its hyperlipemic effect, a high fructose diet has a pro-oxidant effect in rats compared with a starch-based diet. Oligofructose (OFS) has already been shown to decrease plasma lipids in rats. We assessed the impact of fructose on oxidative stress by supplementing a high fructose diet with OFS. Rats were fed either a high fructose diet or a starch-based diet, with or without supplementation of 10 g/100 g oligofructose for 4 wk. Regardless of the type of carbohydrate, OFS in the diet produced an enlargement of the cecum and led to a significant increase in the SCFA cecum pool. Fructose feeding was associated with significantly higher insulin plasma concentrations (+63%) in the control groups, whereas insulin plasma concentrations did not differ in rats fed the fructose diet supplemented with OFS. Plasma leptin concentration was significantly lower (approximately 50%) in the OFS-supplemented fructose group compared with the other three groups. Fructose feeding in rats also significantly increased plasma (P < 0.001) and liver (P < 0.001) triglyceride (TG) concentrations and the addition of OFS prevented the TG accumulation induced by fructose in the liver (P < 0.05) and hyperlipemia (P < 0.05). OFS consumption prevented (P < 0.05) the lower plasma vitamin E/TG ratio in rats fed the fructose diet. Control rats fed the fructose diet had high plasma TBARS values compared with rats fed the starch diet, whereas TBARS values remained unchanged when rats were supplemented with OFS. Control rats fed the fructose diet had higher TBARS urine values and higher heart tissue susceptibility to peroxidation compared with rats fed the starch diet, and this effect was significantly reduced by OFS consumption. Further studies are required to identify the mechanisms underlying the protective effect of OFS against the pro-oxidant effect of fructose. However, the potential nutritional benefits of OFS supplementation in fructose-rich diets are suggested.

Substituting honey for refined carbohydrates protects rats from hypertriglyceridemic and prooxidative effects of fructose

Recent findings indicate that a high fructose diet has a prooxidant effect in rats compared with a starch diet. Because honey is rich in fructose, the aim of this study was to assess the effect of substituting honey for refined carbohydrates on lipid metabolism and oxidative stress. Rats were fed for 2 wk purified diets containing 65 g/100 g carbohydrates as wheat starch or a combination of fructose and glucose or a honey-based diet prepared by substituting honey for refined carbohydrates (n = 9/group). The same amount of fructose was provided by the honey and fructose diets. The hypertriglyceridemic effect of fructose was not observed when fructose was provided by honey. Compared with those fed starch, fructose-fed rats had a lower plasma alpha-tocopherol level, higher plasma nitrite and nitrate (NOx) levels and were less protected from lipid peroxidation as indicated by heart homogenate TBARS concentration. Compared with those fed fructose, honey-fed rats had a higher plasma alpha-tocopherol level, a higher alpha-tocopherol/triacylglycerol ratio, lower plasma NOx concentrations and a lower susceptibility of heart to lipid peroxidation. Further studies are required to identify the mechanism underlying the antioxidant effect of honey but the data suggest a potential nutritional benefit of substituting honey for fructose in the diet.

The relationship between lipoprotein lipase activity and respiratory quotient of rats in circadian rhythms

Plasma lipid levels and lipoprotein lipase (LPL) are known to follow circadian rhythms in rats. However, very little information is available on the variations in respiratory quotient (RQ) during the 24-h period in rats. The aims of this study were to provide an overall view of the effects of circadian rhythm on RQ and to determine the relationship of LPL and RQ with metabolic parameters in these animals. Male rats were fed ad libitum and were kept under a 12 :12-h light-dark cycle. Rats were killed every 2 h over a 24-h period for measurement of metabolic parameters and tissue LPL activity. The RQ was measured every 4 h over the same 24-h period. The gastric contents increased during the dark phase and decreased during the light phase. For the metabolic parameters, circadian rhythms were detected for plasma glucose, triglycerides, high-density lipoprotein cholesterol and non esterified free fatty acids, but not for plasma total cholesterol or phospholipids. The RQ and adipose tissue LPL activity increased during the dark phase, while skeletal muscle LPL activity decreased during this phase. The RQ was inversely correlated with skeletal muscle LPL activity (r = -0.880) and positively correlated with adipose tissue LPL activity (r = 0.937). These results appear to show that rats tend toward consumption of fat by accelerating fat oxidation, resulting in suppression of fat accumulation in the light phase, while tending toward fat accumulation by the suppression of fat oxidation in the dark phase.

Hypotriglyceridemic effect of Anka (a fermented rice product of monascus sp.) in rats

Experimental rats with hypertriglyceridemia were prepared by feeding a high-fructose diet. Dried Anka powder (2%), a rice product fermented with Monascus sp., was mixed with basic high-fructose (30%) or basal-diet feed. Serum and liver lipids were measured after 6 months. The concentrations of serum triglycerides, total cholesterol, VLDL-C, and LDL-C had significantly decreased, whereas that of HDL-C had slightly increased in 30% fructose-Anka-fed rats as compared with the 30% fructose-fed rats, but hepatic lipase activity had increased in the Anka-fed groups. The ratio of lipoprotein lipase/hepatic lipase was not significantly different between 30% fructose-Anka-fed rats and 30% fructose-fed rats. The dietary intake and weight of these two groups were approximately the same. Similar results were obtained in noninduced hypertriglyceridemic rats. The concentrations of triglycerides and cholesterol did not significantly differ in the liver. Interestingly, Anka can suppress serum triglycerides in rats with induced hypertriglyceridemia. The antioxidant enzyme SOD activity was also measured in serum, and no significant change was observed. On the basis of these findings, we suggest that Anka may be used to suppress hypertriglyceridemia and hyperlipidemia in rats and possibly in man.

Effect of increased afterload on cardiac lipoprotein lipase and VLDL receptor expression

Fatty acids are a major source of fuel for energy production by myocytes. Lipoprotein lipase (LPL) and very low density lipoprotein (VLDL) receptor are abundantly expressed by the heart and skeletal muscles. LPL and possibly VLDL receptor represent the primary route of access to fatty acids contained in circulating triglyceride-rich lipoproteins. Physical exercise and thyroid hormone, which promote energy consumption, upregulate LPL expression in skeletal muscles. This study tested the hypothesis that increased cardiac workload might modulate myocardial LPL and/or VLDL receptor expressions. Accordingly, cardiac tissue LPL activity, LPL and VLDL receptor proteins and mRNA abundance were studied in Sprague-Dawley rats 4 weeks after induction of severe thoracic aorta constriction or sham operation. Elevation of afterload with thoracic aortic constriction led to a significant cardiomegaly and a marked upregulation of cardiac LPL activity, LPL mRNA and LPL protein abundance, but did not modify VLDL receptor mRNA or protein abundance. Thus, increased cardiac workload in this model results in upregulation of myocardial LPL expression which can enhance fatty acid availability to accommodate the heart's increased energy requirement.

Lipoprotein lipase and the disposition of dietary fatty acids

Lipoprotein lipase (EC 3.1.1.34; LPL) is a key enzyme regulating the disposal of lipid fuels in the body. It is expressed in a number of peripheral tissues including adipose tissue, skeletal and cardiac muscle and mammary gland. Its role is to hydrolyse triacylglycerol (TG) circulating in the TG-rich lipoprotein particles in order to deliver fatty acids to the tissue. It appears to act preferentially on chylomicron-TG, and therefore may play a particularly important role in regulating the disposition of dietary fatty acids. LPL activity is regulated according to nutritional state in a tissue-specific manner according to the needs of the tissue for fatty acids. For instance, it is highly active in lactating mammary gland; in white adipose tissue it is activated in the fed state and suppressed during fasting, whereas the reverse is true in muscle. Such observations have led to the view of LPL as a metabolic gatekeeper, especially for dietary fatty acids. However, closer inspection of its action in white adipose tissue reveals that this picture is only partially true. Normal fat deposition in adipose tissue can occur in the complete absence of LPL, and conversely, if LPL activity is increased by pharmacological means, increased fat storage does not necessarily follow. LPL appears to act as one member of a series of metabolic steps which are regulated in a highly coordinated manner. In white adipose tissue, it is clear that there is a major locus of control of fatty acid disposition downstream from LPL. This involves regulation of the pathway of fatty acid uptake and esterification, and appears to be regulated by a number of factors including insulin, acylation-stimulating protein and possibly leptin.