A novel assay for triglycerides using glycerol dehydrogenase and a water-soluble formazan dye, WST-8

Background

The glycerol-3-phosphate (GPO)-peroxidase (POD) chromogenic method is one of the most widely used methods to assay triglycerides. However, it is well known that peroxidase is affected by reducing agents, and recently, it has been reported that some materials affect its activity. Moreover, there is a high possibility of non-specific reaction, as the method uses many enzymes. Against this background, we developed a simpler assay method for triglycerides without using peroxidase.

Methods

Triglycerides were hydrolysed to glycerol and fatty acids by lipoprotein lipase followed by the oxidation of glycerol to dihydroxyacetone with simultaneous production of NADH by glycerol dehydrogenase. To overcome incomplete conversion of glycerol to dihydroxyacetone by glycerol dehydrogenase at equilibrium, we added 2-(2-methoxy-4-nitrophenyl)-3–(4-nitrophenyl)-5–(2,4-disulfophenyl)-2 H-tetrazolium monosodium salt (WST-8) to the reaction mixture to remove NADH, allowing the reaction to complete while showing stoichiometric production of reduced WST-8.

Results

The reaction was linear up to 6.4 mmol/L. The mean intra-assay ( n = 20) and inter-assay ( n = 20) imprecision, as determined by replicate analysis of three pooled human serum samples with different triglyceride concentrations, were 1.1–2.3% and 1.1–1.5% coefficient of variation (%CV), respectively. No interference by 2.5 g/L haemoglobin, 65  μmol/L free bilirubin and 359  μmol/L conjugated bilirubin was observed. The equation obtained in comparison with that by the GPO-POD method including endogenous glycerol-eliminating step was: y = 1.0002x + 0.0395 mmol/L; r = 0.999; Sy/x = 0.049 mmol/L; n = 97.

Conclusion

Our method is an accurate, yet simpler and more sensitive for the quantitative analysis of triglycerides.

Chamnamul [Pimpinella brachycarpa (Kom.) Nakai] ameliorates hyperglycemia and improves antioxidant status in mice fed a high-fat, high-sucrose diet

Chronic consumption of a high-fat, high-sucrose (HFHS) diet increases insulin resistance and results in type 2 diabetes mellitus in C57BL/6J mice. Hyperglycemia in diabetics increases oxidative stress, which is associated with a high risk of diabetic complications. The purpose of this study was to examine the hypoglycemic and antioxidant effects of chamnamul [Pimpinella brachycarpa (Kom.) Nakai] in an animal model of type 2 diabetes. The α-glucosidase inhibitory activity of a 70% ethanol extract of chamnamul was measured in vitro. Five-week-old male C57BL/6J mice were fed a basal or HFHS diet with or without a 70% ethanol extract of chamnamul at a 0.5% level of the diet for 12 weeks after 1 week of adaptation. After sacrifice, serum glucose, insulin, adiponectin, and lipid profiles, and lipid peroxidation of the liver were determined. Homeostasis model assessment for insulin resistance (HOMA-IR) was determined. Chamnamul extract inhibited α-glucosidase by 26.7%, which was 78.3% the strength of inhibition by acarbose at a concentration of 0.5 mg/mL. Serum glucose, insulin, and cholesterol levels, as well as HOMA-IR values, were significantly lower in the chamnamul group than in the HFHS group. Chamnamul extract significantly decreased the level of thiobarbituric acid reactive substances and increased the activities of superoxide dismutase, catalase, and glutathione peroxidase in the liver compared with the HFHS group. These findings suggest that chamnamul may be useful in prevention of hyperglycemia and reduction of oxidative stress in mice fed a HFHS diet.

Lotus leaf alleviates hyperglycemia and dyslipidemia in animal model of diabetes mellitus

The purpose of this study was to investigate the effects of lotus leaf on hyperglycemia and dyslipidemia in animal model of diabetes. Inhibitory activity of ethanol extract of lotus leaf against yeast α-glucosidase was measured in vitro. The effect of lotus leaf on the postprandial increase in blood glucose levels was assessed in streptozotocin-induced diabetic rats. A starch solution (1 g/kg) with and without lotus leaf extract (500 mg/kg) was administered to the rats after an overnight fast, and postprandial plasma glucose levels were monitored. Four-week-old db/db mice were fed a basal diet or a diet containing 1% lotus leaf extract for 7 weeks after 1 week of acclimation to study the chronic effect of lotus leaf. After sacrifice, plasma glucose, insulin, triglycerides (TG), total cholesterol (CHOL), high-density lipoprotein (HDL)-CHOL, and blood glycated hemoglobin levels were measured. Lotus leaf extract inhibited α-glucosidase activity by 37.9%, which was 1.3 times stronger than inhibition by acarbose at a concentration of 0.5 mg/mL in vitro. Oral administration of lotus leaf extract significantly decreased the area under the glucose response curve by 35.1% compared with that in the control group (P < 0.01). Chronic feeding of lotus leaf extract significantly lowered plasma glucose and blood glycated hemoglobin compared with those in the control group. Lotus leaf extract significantly reduced plasma TG and total CHOL and elevated HDL-CHOL levels compared with those in the control group. Therefore, we conclude that lotus leaf is effective for controlling hyperglycemia and dyslipidemia in an animal model of diabetes mellitus.

Antiplasmodial activity of two marine polyherbal preparations from Chaetomorpha antennina and Aegiceras corniculatum against Plasmodium falciparum

The ocean covers more than 70% of earth surface and hosts most 300,000 described species of plants and animals to use, which have been virtually unexploited for the development of medicines. Marine plants are the good source of biologically active entities which exhibit therapeutic properties, when applied single or in combination of different plant extracts (polyherbal). Polyherbal preparations are always a complex mixture of different forms and thus different compounds, which might act as agonistic, synergistic, complementary, antagonistic or toxic way. The present study was initially carried out to test the antiplasmodial activity of 13 mangrove plants and eight seaweeds species distributed along the coast of south India. Of these, mangrove species Aegiceras corniculatum and the seaweed species Chaetomorpha antennina have shown maximum antiplasmodial activity. Hence, the present study was mooted out to increase the percentage of antiplasmodial activity when applied as polyherbal preparations. The effect of marine polyherbal preparations from the methanolic extracts of two marine plants A. corniculatum and C. antennina for their antiplasmodial activity was tested. It shows that the polyherbal extract showed 63.50 ± 0.408% suppression of parasitaemia against Plasmodium falciparum at 1.5 mg ml⁻¹ concentration. In vivo test was carried out with rat animal model to find out the effectiveness of the polyherbal extracts in the live system, which reveals that polyherbal extracts have exhibited remarkable antiplasmodial activity (50.57 ± 0.465%) against Plasmodium berghei at 120 mg kg⁻¹ bw. This study shows that combinations of mangrove plants and seaweeds extracts had a source of lead compounds for the development of new drugs for the treatment of malaria.

Evaluation of the hypolipemic property of Camellia sinensisVar. ptilophylla on postprandial hypertriglyceridemia

A naturally decaffeinated tea, Camellia sinensis var. ptilophylla (cocoa tea), has long been popular in southern China as a healthy beverage. Our experiments indicate that a single oral administration of 500 mg/kg of cocoa tea extract suppresses increases in plasma triacylgycerol (TG) levels when fed with 5 mL/kg of olive or lard oil in mice and that the inhibition rates are 22.9% and 31.5%, respectively, compared with controls. Under the same condition, cocoa tea extract did not affect the level of plasma free fatty acid. Likewise, the extract reduced the lymphatic absorption of lipids at 250 and 500 mg/kg. Also, cocoa tea extract and polyphenols isolated from cocoa tea inhibit pancreatic lipase. These findings suggest that cocoa tea has hypolipemic activity, which may be due to the suppression of digestive lipase activity by the polyphenols contained within the tea.

Hypolipemic effect of Cyclocarya paliurus (Batal) Iljinskaja in lipid-loaded mice

We investigated the inhibitory effect of Cyclocarya paliurus (Batal.) Iljinskaja (C. paliurus) extract on postprandial hyperlipemia in mice. A single oral administration of C. paliurus extract (250 mg/kg) suppressed an increase in plasma triacylgycerol (TG) levels when fed with 5 ml/kg of lard and olive oil. The inhibition rates were 28.6% and 24.1%, respectively, but free fatty acid (FFA) levels in plasma were not significantly affected as compared with control group mice. In addition, C. paliurus extract showed inhibitory activity toward pancreatic lipase, a key enzyme of dietary TG absorption, with an IC(50) of 9.1 microg/ml in vitro. Our results suggested that the hypolipemic action of C. paliurus extract was probably interrelated with suppression of the activity of digestive lipase, and as a result, the blood lipid level was reduced.

Effects of repeated gestation and lactation on milk n-6 fatty acid composition in rats fed on a diet rich in 18:2n-6 or 18:3n-6

The present study examined the effect of repeated gestation and lactation on the levels of long-chain n-6 polyunsaturated fatty acids in rat milk fat, and examined whether such levels might be modulated by supplementing the diet of the lactating dams with either (g/kg) 50 safflower oil (SFO; containing 800 g 18:2n-6/kg), or 50 evening primrose oil (EPO; containing 720 g 18:2n-6 and 90 g 18:3n-6/kg). The milk was collected at three different times (days 1, 8 and 15) in each given lactation period from female Sprague-Dawley rats which were successively bred for four pregnancies and lactations. Results showed that dietary fat and breeding frequency had no significant effects on milk triacylglycerol content, but they modified the pattern of milk fatty acids in both triacylglycerol and phospholipid fractions. After three or four successive breedings rats fed on EPO produced milk containing less saturated but more monounsaturated and polyunsaturated fatty acids compared with those fed on SFO. During the course of lactation the levels of n-6 metabolites, e.g. 18:3n-6, 20:3n-6 and 20:4n-6, in milk fat declined progressively. However, they were consistently higher in the EPO group than in the SFO group. These findings suggest that the levels of long-chain n-6 metabolites in the milk fat may be increased through supplementing the maternal diet with 18:3n-6.

Short-term effects of fat emulsion on serum lipids in postoperative patients

The effect of short-term infusion of intravenous fat on serum lipids was assessed in 23 patients who had elective cancer operations and were given 20% Intralipid for 5 days postoperatively as part of a standard total parenteral nutrition regimen. Serum lipids were measured prior to, during and after the 5-day infusion period. The percentage of cholesterol as high-density lipoproteins (HDL) fell from a mean preinfusion value of 34.7 +/- 2.8 to 27.9 +/- 2.5 (p less than 0.05), while the percentage of cholesterol as low-density lipoproteins (LDL) increased from 40.7 +/- 2.2 to 46.8 +/- 3.4 (p less than 0.05). Serum triglycerides fell significantly (p less than 0.01) from 106.2 +/- 13.7 mg/dl to 64.6 +/- 8.8 mg/dl at 3 days, being 85.3 +/- 3.7 mg/dl at 5 days. No significant change in percent cholesterol as very low-density lipoproteins (VLDL), or levels of serum total cholesterol or phospholipids occurred. Lipoprotein X was detectable in six patients after 5 days. To study triglyceride clearance 1.7 g/kg of fat emulsion was infused over 8 hr and serial blood samples obtained. Within 3 hr of stopping the fat infusion, triglyceride levels had fallen to preinfusion values.

Study of the components of reverse cholesterol transport in lecithin:cholesterol acyltransferase deficiency

Enzymatic and lipid transfer reactions involved in reverse cholesterol transport were studied in healthy and lecithin:cholesterol acyltransferase (LCAT), deficient subjects. Fasting plasma samples obtained from each individual were labeled with [3H]cholesterol and subsequently fractionated by gel chromatography. The radioactivity patterns obtained corresponded to the elution volumes of the three major ultracentrifugally isolated lipoprotein classes (very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)). In healthy subjects, the LCAT activity was consistently found in association with the higher molecular weight portion of HDL. Similar observations were made when exogenous purified LCAT was added to the LCAT-deficient plasma prior to chromatography. Incubation of the plasma samples at 37 degrees C resulted in significant reduction of unesterified cholesterol (FC) and an increase in esterified cholesterol (CE). Comparison of the data of FC and CE mass measurements of the lipoprotein fractions from normal and LCAT-deficient plasma indicates that: (i) In normal plasma, most of the FC for the LCAT reaction originates from LDL even when large amounts of FC are available from VLDL. (ii) The LCAT reaction takes place on the surface of HDL. (iii) The product of the LCAT reaction (CE) may be transferred to either VLDL or LDL although VLDL appears to be the preferred acceptor when present in sufficient amounts. (iv) CE transfer from HDL to lower density lipoproteins is at least partially impaired in LCAT-deficient patients. Additional studies using triglyceride-rich lipoproteins indicated that neither the capacity to accept CE from HDL nor the lower CE transfer activity were responsible for the decreased amount of CE transferred to VLDL and chylomicrons in LCAT-deficient plasma.

A fluorometric method for the determination of triglycerides in nanomolar quantities

A fluorometric assay for triglycerides in nanomole quantities is described. Glycerol is liberated from triglycerides with lipase from Chromobacter viscosum, then converted by glycerol kinase to glycerol-3-phosphate, which is oxidized by glycerol-3-phosphate oxidase, producing H2O2. The H2O2 ultimately forms a peroxidase-catalyzed fluorogen with p-hydroxyphenylacetic acid. The excitation and emission wavelengths of the fluorogen are 325 and 415 nm, respectively. The assay is linear in the range 0.05-35 nmol of triglycerides using triolein as standard.

A simple enzymatic fluorimetric method for the determination of triglycerides in 10 microliters of serum

An assay for the determination of triglyceride (acyl glycerol) in microliter volumes of serum or plasma is described. The method is based on enzymatic hydrolysis of triglyceride by lipase from Rhizopus arrhizus followed by enzymatic fluorimetric assay of the glycerol so released. Under the conditions of the assay the enzymatic hydrolysis is complete for concentrations up to 5 mmol/l in less than 15 min at room temperature. The determination of free glycerol and glycerol released is based on the formation of dihydroxyacetone in the presence of NAD and glycerol dehydrogenase. The NADH which is formed in stoichiometric quantities is estimated fluorimetrically. In the presence of the ketone-trapping agent hydrazine the reaction goes to completion above pH 9.0. By this method acyl glycerol can be measured routinely in a 10 microliters sample of serum or plasma. The test is extremely sensitive compared to previously described methods and exhibits acceptable precision and reproducibility.

A sensitive kinetic assay for glycerol using bacterial bioluminescence

A kinetic assay method based on bacterial bioluminescence and the glycerol dehydrogenase (GDH) enzyme reaction has been developed for the determination of glycerol. The assay system involves the use of three coupled enzyme reactions in which the participating reactants are optimized to allow internal calibration by known amounts of glycerol. This bioluminescent assay method is also suitable for measuring GDH enzyme activity. The lower detection limit for glycerol is 500 pmol and for GDH, 0.001 mU, the assay being linear up to 300 nmol of glycerol and 3 mU of GDH. The percentage recovery of glycerol from serum was 95-100%. This assay method is rapid, sensitive, and reproducible.

A simple one-step enzymatic fluorometric method for the determination of glycerol in 20 microliters of plasma

An assay for the determination of glycerol concentration in blood or other biological materials is described. The method is based on the conversion of glycerol to dihydroxyacetone in the presence of NAD, the reaction being catalysed by the enzyme glycerol dehydrogenase. The NADH which is formed in stoichiometric quantities during the reaction is estimated fluorometrically. In the presence of the ketone-trapping agent hydrazine the reaction can be made to go to completion above above pH 9.0. Using the method described, glycerol can be measured routinely in a 20-microliters sample of serum or plasma. Although the enzyme is known to react with sorbitol and ethanol, the addition of these substances to the reaction mixture had no significant effect on the determination of glycerol.

Fully enzymic method of plasma triglyceride determination using an immobilized glycerol dehydrogenase nylon-tube reactor

A new, enzymic method of triglyceride determination in serum and plasma by use of an immobilized glycerol dehydrogenase nylon-tube reactor, integrated into the flow system of an AutoAnalyzer II (Technicon) is described. The combination of this reactor, stable for 1500--2000 tests, with the lipolytic enzymes which are added in solution yields a reliable and reproducible assay, which correlates well with the commonly used fully enzymic triglyceride determination. Using this new method, the cost can be reduced to about one-third of that of the other method.

Enzymatic determination of triglycerides with a system Olli 3000 analyser

We describe a totally enzymatic method for determining serum triglycerides adapted for a System Olli 3000 analyser. In this procedure triglycerides are determined by measuring free glycerol enzymatically after hydrolysis of a sample with lipase and esterase. The method utilizes two standards for calibration, includes a blank correction and requires 20 microliter of serum. Forty serum samples can be analysed in about 30 min. The procedure is linear up to a concentration of 8 mmol/l of triglycerides. The precision and sensitivity of the method are good. A comparison of this method with another enzymatic method gave the correlation coefficient 0.988 and the regression line y = 1.02x + 0.02 (n = 95).

A simple colorimetric method for determination of serum triglycerides with lipoprotein lipase and glycerol dehydrogenase

A simplified enzymic procedure to determine accurately serum triglycerides is described. Serum triglycerides are hydrolyzed completely to free fatty acids and glycerol by lipoprotein lipase from Pseudomonas fluorescens. The released glycerol is oxidized with glycerol dehydrogenase from Erwinia aroideae in the presence of NAD+, were the reduction of the enzyme-linked NAD+ is coupled to the reduction of nitro blue tetrazolium as a chromogenic indicator with phenazine methosulfate serving as an intermediate electron carrier of NADH. The absorbance at 570 nm is measured. The method requies only 20 microliter of serum and a 10-min incubation and is rapid and simple. The present method offers the measurement of a high concentration of triglyceride up to 1000 mg/dl serum. The results obtained by the present method show good correlation with those obtained by the glycerol kinase method (correlation coefficient, 0.989) or the acetylacetone method (correlation coefficient, 0.979). These results suggest that the proposed method will be utilized as a method or routine clinical test.