Effect of flavonoids morin; quercetin and nicotinic acid on lipid metabolism of rats experimentally fed with triton

Effect of Flavonoids Morin; Quercetin and Nicotinic Acid on Lipid Metabolism of Rats Experimentally Fed with Triton

Kelly Fabiane Santos Ricardo¹, Tânia Toledo de Oliveira¹, Tanus Jorge Nagem2^*, Aloisio da Silva Pinto³, Maria Goreti Almeida Oliveira¹ and José Francisco Soares⁴

1Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Viçosa, 36571-000; Viçosa - MG, Brazi; ²Departamento de Química da Universidade Federal de Ouro Preto, 35400-000; Ouro Preto - MG, Brazil; ³Departamento de Veterinária da Universidade Federal de Viçosa, 36571-000; Viçosa - MG, Brasil; Departamento de Matemática e Estatística da Universidade Federal de Minas Gerais, 31270-000; Belo Horizonte - MG, Brasil

ABSTRACT

Atherosclerosis is a coronary disease where deposition of lipids in the arteries leads to problems of blood circulation. The present work evaluates the action of the flavonoids morin, quercetin and nicotinic acid isolated in association on lipid metabolism in hyperlipidemic rats. Blood serum levels cholesterol, cholesterol-HDL, and triacylglycerids have been analysed following the intraperitoneal administration of the flavonoid compounds dissolved in propyleneglycol by in doses of 5mg/kg body weight. Quercetin presented the largest percentual reduction of cholesterol. The best results for cholesterol-HDL have been obtained with-nicotinic acid alone while morin-nicotinic acid combination showed the best triacylglycerols results. Results showed that flavonoids could be beneficious in the treatment of coronary diseases.

Key words: Morin, Quercetin, Nicotinic Acid, Lipid, Cholesterol, Cholesterol-HDL, Triacylglycerols, Rats, Hyperlipidemic

INTRODUCTION

Arterial hypertension, tobaccoism, hypercholesteraemia, obesity, intolerance to glucose (insulinic resistance), hipertryglyceridaemia, low levels of blood cholesterol-HDL (<35 mg/dl), elevated levels of a-lipoproteins, rich diet ingestion (excessive and regular ingestion of cholesterol, saturated fat and refined sugar), hyperuricemia and elevated levels of fibrinogen in the blood are regarded as main causes of cardiovascular diseases. Successive treatments to prevent atherosclerosis combine lifestyle alterations, pharmacological interventions (impaired platelets, antihypertensives drugs, anticoagulants, beta-blockers, estrogenic therapy) and vascular surgeries (Leite, 1994).

Considering treatments the flavonoids, a group of polyphenolic compounds found mainly in plants of the leguminosae family, have been shown to exhibit a series of biological effects among which stand out the inhibition of lipid peroxidation and platelet aggregation, due to their antioxidant properties and their ability of removing free radicals and chelating divalent cations (Cavallini et al, 1978, Lackeman et al, 1986, Fraga et al, 1987, Affana’s et al, 1989, Hanasaki et al, 1994, Frankel et al, 1993).

Since the discovery that Triton WR 1339 causes hyperlipidemia in experimental animals, the detergent has widespread use as a tool for studying lipid metabolism (Kellner et al, 1951, Recknagel, 1967). Early investigators exploited its capacity to block lipid clearance for measuring rates of triglyceride and cholesterol synthesis and, more recently, the inhibitory action of the detergent has been usefully employed for investigating metabolic interrelationships between plasma lipoproteins. We felt that Triton WR 1339 may also prove useful for studying the involvement of apoproteins in triglyceride catabolism since any changes in the composition or concentration of these proteins may be related to the delay in triglyceride catabolism that follows administration of the detergent. Some of the factors that are know to be important in the catabolism of very low density lipoprotein are the peptide components of high density lipoprotein, specifically the A-I and C-II apoproteins. The firs of these (A-I) activates lecithin: cholesterol acyl transferase, an enzyme which is considered responsible for the formation of most of the serum cholesterol esters and which, in cooperation with lipoprotein lipase, is thougth to take part in the conversion of VLDL to the Cholesterol ester rich low density lipoprotein LDL (Ishikawa et al, 1979).

One of their effects is the prevention of the atherogenic oxidation of cholesterol-LDL (Steinberg et al, 1989). However, flavonols and flavones can also inhibit the lipoxygenase (Hope et al, 1983), decreasing the platelet aggregation and reducing thrombocitic tendencies (Gryglewski et al, 1987 and Tzeng et al, 1991).

Jahromi and Ray (1993) observed that pterosupin and liquirritigenin were able to reduce cholesterol, cholesterol-LDL and triacylglycerol levels in Triton-induced hyperlipemic rats. Nicotinic Acid is already part of the therapeutic arsenal for lipid control in humans showing reductive effects on cholesterol, triacylglycerols and cholesterol-LDL while increasing cholesterol-HDL (Seed et al, 1993).

The present work aimed to evaluate the effects of the flavonoids morin, quercetin and nicotinic acid alone and in association on the control of lipid metabolism.

MATERIAL AND METHODS

In this study male rats of the "Wistar" race, provided by the Department of Nutrition of the Federal University of Viçosa, weighing 200±20g, were used. They received commercial ration Labina and water ad libitum. After an adaptation period of five days to cages with controlled periods of light and darkness of 12 hours, the animals were separated in seven experimental groups eight animals each. They were randomly distributed to receive the treatments as shown in Table 1. Experimental delimitation was entirely randomised for the seven treatments with eight repetitions.

In order to induce hyperlipemia, Triton (Sigma), dissolved in a physiologic solution of NaCl (0,9%) was administered intraperitoneally in rats in doses of 300 mg/kg body weight. After 24 hours morin, quercetin and nicotinic acid (Sigma) were administered alone and or association as shown on Table 1. These compounds were dissolved in propyleneglycol and supplied intraperitoneally in doses of 5 mg/kg body weight. After another 24 hours, the animals were anaesthetised by inhalation of ethyl ether and blood samples were taken via heart puncture. The samples were centrifuged at 7100g during 15 minutes in order to obtain the serum which was analysed for cholesterol and triacylglycerols following the method described by Henry (1982) and cholesterol-HDL following the method described by Lima et al. (1985). Quantitative analysis carried out using a Hitachi spectrophotometer.

Statistical interpretation was carried out using Tuckey and Dunnet tests.

RESULTS AND DISCUSSION

Tables 2, 3 and 4 show the results obtained from analysing the serum samples. The effects of the different treatments are expressed as percentual variations of the serum lipid values from the control group 2 of Triton-induced hyperlipemic rats.

According to the results in Table 2 the animals treated with Triton (group 2), showed a 10-fold increase of average serum cholesterol levels. When submitted to the different treatments, these hypercholesteremic animals showed statistically significant reductions of their cholesterol levels. Among the treatments carried out, quercetin (group 4) presented the largest percentual reduction in comparison with group 2, as shown by the Dunnet test. These results are in accordance with literature (Maggio, 1956 and Kato & Tosa, 1983). After statistical classification with Tuckey test, it was observed that groups 3,4 and 6 differed only at a level of 5% probability.

The results on cholesterol-HDL shown in Table 3 showed that the best treatment was obtained with nicotinic acid alone (group 5) as deduced by Tuckey test. This group also showed the best results in the deduction using Dunnet test since it lowered the levels of cholesterol- HDL only by –4.24 %, which was of benefit since cholesterol-HDL has been responsible for the transport of cholesterol from peripheric circulation to the liver where it is metabolized.

The effects on the increase of cholesterol-HDL are in accordance with results shown in literature (Seed et al, 1993), where humans were treated with nicotinic acid. The mechanism of this action is known as inhibiting the lipolysis in the adipose tissue, reducing the esterification of triacylglycerids in the liver, and increasing the activity of the lipoproteic lipase (Witztum, 1996).

Table 4 presents the results of rat serum triacylglycerids. It was found that the treatment with nicotinic acid and morin (group 6) presented the largest percentual reduction of the levels of Triacylglycerids (derived from the Tukey Test) although the other treatments have been statistically significant as well. Group 6 also showed the best results when deduced with Dunnet test. However, the variation of the results of the other tratments were small.

Literature registers that biochanin A and formonometin reduce the triacylglycerols levels in 35.6% and 23.5%, tested in male albino rats with hyperlipidemia induced by triton WR-1369 (Siddiqui & Siddiqui, 1996).

Studies accomplished about the relationship structure-activity of flavonoids on inhibition of lipid peroxidation explained their mechanism of action being based on their structure. The presence of the hydroxyl group at C-3 position of the skeletons of quercetin, miricetin, catequin and morin has been shown to be responsible for the potent inhibitory action on lipid peroxidation (Affana’s et al, 1989; Ratty & Das, 1988; Mora et al, 1990; Morel et al, 1993). When the double bond between the carbons 2 and 3 of the C ring is hydrogenated, antiperoxidative potential decreases (Cavallini et al, 1978; Ratty & Das, 1988; Cholbi et al, 1991). The carbonyl group at C-4 position is essential for the antiperoxidant activity (Cavallini et al, 1978; Ratty & Das, 1988; Morel et al, 1993). The number of hydroxyl groups in the rings A and B of flavonoids has been shown to be important in the protection against free radicals. It has been shown that the more hydroxyl groups are substituted in the B-ring , mainly at C-3', the higher is the antiperoxidative activity (Husain et al, 1987). The hydroxyl groups at the C-5 and C-7 positions of the A-ring and C-3’and C-4’ of the B-ring and C-3 of the C-ring seem to contribute to the antioxidant action (De Whalley et al, 1990). The flavonoids that have hydroxyl groups at C-2’ position, such as morin, have shown antiperoxidative properties (Cholbi et al, 1991). The hydroxyl groups at the C-3 and C-5 of the flavonoid skeleton, like in quercetin and morin, besides the carbonyl group at C-4 can form chelators for iron ions. The ability of flavonoids to kidnap metallic ions contributes to their antiperoxidatives properties, preventing the formation of free radicals (Affana’s et al, 1989; Mora et al, 1990).

It could be concluded that quercetin and morin showed potential activities in the reduction of cholesterol and triacylglycerid levels alone or in combination with nicotinic acid, although they have not been so effective in maintaining the levels of cholesterol-HDL.

RESUMO

Aterosclerose é uma doença coronária onde a deposição de lipídeos nas artérias leva a problemas na circulação sangüínea. O presente trabalho avalia a ação dos flavonóides morina, quercetina e ácido nicotínico isoladamente e em associação no metabolismo lipídico em ratos hiperlipidêmicos. Foram analisados os níveis de colesterol, colesterol- HDL e triacilgliceróis no soro sangüíneo após administração, via intraperitoneal, dos compostos flavonoídicos dissolvidos em propileno glicol na dose de 5mg/kg de peso corporal. Quercetina mostrou o maior percentual de redução do colesterol. Para colesterol-HDL, os melhores resultados foram obtidos com ácido nicotínico isoladamente, enquanto a associação morina-ácido nicotínico mostrou os melhores resultados para triacilgliceróis. Os resultados mostraram que os flavonóides podem ser benéficos no tratamento de doença coronoriana.

Received: June 17, 1999;

Revised: September 13,1999;

Accepted: November 26, 2000.

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^*

Author for correspondence

Publication Dates

• Publication in this collection
  23 Jan 2002
• Date of issue
  Sept 2001

History

• Accepted
  26 Nov 2000
• Reviewed
  13 Sept 1999
• Received
  17 June 1999