- Email: [email protected]
Pharmacological effects of garlic extract
Update
62
TRENDS in Pharmacological Sciences
number of side-effects will merit comparison with metabolites of some of the 2700 isoforms of cytochromes P450 as a model for the drug-binding choices of these enzymes and the transiency of a receptor conformation [5]. It is generally recognized that, overall, the lowest energy conformations that are stable are, at present, largely unpredictable for proteins (including enzymes and receptors). Therefore, the existence of multiple conformations of receptors (provided by multiple domains), some of which do not affect the putative main ligand binding site, cannot be ignored both in silico and in the laboratory [3] if we are to eliminate most of the distressing side-effects produced by therapeutic, particularly neuroleptic, drugs.
Vol.24 No.2 February 2003
References 1 Kenakin, T. and Onaran, O. (2002) The ligand paradox between affinity and efficacy: can you be there and not make a difference? Trends Pharmacol. Sci. 23, 275– 280 2 Palmer, T. (2001) Enzymes: Biochemistry, Biotechnology, Clinical Chemistry, Horwood Publishing, Chichester, UK 3 Wiseman, A. and Woods, L.F.J. (2002) Can ‘real-lab’ supersede ‘virtualligand’ promises? Trends Pharmacol. Sci. 23, 261 4 Wiseman, A. et al. (2002) Are food and environmental toxicants ‘overdetected’ by bioassay? Trends Biotechnol. 20, 13 – 15 5 Wiseman, H. et al. (2000) Biomolecular Free Radical Toxicity: Causes and Prevention, John Wiley and Sons
0165-6147/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0165-6147(02)00047-0
Pharmacological effects of garlic extract Ruomei Qi1 and Zhengang Wang2 1 2
Beijing Institute of Geriatrics, Beijing Hospital Ministry of Health, No.1 Dahualu Beijing 100730, China Institute of Basic Medical Science, Beijing Union Medical College and Chinese Academy of Medical Science, Beijing, China
Garlic has been used as a herbal medicine for thousands of years. Recent studies have demonstrated that garlic contains several medically active substances that possess many favorable effects, such as a decrease in low-density lipoprotein (LDL), antioxidation, anti-thrombosis and suppression of platelet aggregation. In recent years, it has become apparent that an increasing number of people prefer to take natural medicines rather than chemical synthetics. Thus, research into natural garlic extract has attracted greater attention. Oxidative modification of DNA is related to aging and diseases such as cardiovascular diseases, neurodegenerative diseases and even cancer. Garlic extract exhibits antioxidant action by increasing the levels of cellular antioxidant enzymes, such as superoxide dismutase, catalase and glutathione peroxidase, and scavenging reactive oxygen species [1], and thus might have some benefit in diseases in which reactive oxygen species play a part. Oxidation of LDL is an important process in the development of atherosclerosis. Recent studies have demonstrated that garlic extract can inhibit LDL oxidation in vitro, reduce plasma LDL in vivo and retard atherogenesis in rabbits. It is therefore reasonable to suggest that garlic extract might be useful in the prevention of the progression of atherosclerosis in humans. Platelets play a crucial role in thrombosis and, indeed, the prevention and treatment of thrombosis is focused mainly on the inhibition of platelet function. Garlic extract has been shown to suppress platelet aggregation strongly by inhibiting intracellular Ca2þ mobilization and thromboxane A2 (TXA2) generation. TXA2 is a metabolic product of arachidonic acid and an endogenous stimulant of platelet activity. Inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3], a well known intercellular second messenger, can mediate Corresponding author: Ruomei Qi ([email protected]). http://tips.trends.com
Ca2þ release following activation of phospholipase C by certain agonists. Garlic extract, however, exerts its action through neither the inhibition of the generation of Ins(1,4,5)P3 nor Ca2þ-depletion-induced Ca2þ influx, but by the inhibition of Ca2þ mobilization. It therefore proposed that garlic extract might act downstream of Ins(1,4,5)P3 [2]. Ajoene, a garlic-derived natural compound, has been shown to induce apoptosis in leukemic cells in addition to other blood cells of leukemic patients. Ajoene induces apoptosis in human leukemic cells via stimulation of peroxide production and activation of nuclear factor kB. This new biological effect might elucidate the molecular mechanism of the anti-tumor action of ajoene [3]. Ajoene also affects apoptosis by activation of caspase-3-like activity and caspase-8 activity in leukemic cell lines. Another study demonstrated that purified allicin (another major compound of garlic extract) inhibited proliferation of human mammary (MCE-7) endometrial and colon (HT-29) cancer cells. The inhibition of growth was accompanied by an accumulation of the cell in G0/G1 and G2/M phase of the cell cycle and not by a significant increase in cell death. This result implies that allicin is responsible for the antiproliferative effect of garlic extract [4]. Taken together, the beneficial effects of garlic extract make it useful in health care. Many countries have used garlic extract for clinical treatments, but the untoward actions of garlic extract following long-term administration should be fully noted. Even though many studies on garlic extract have been performed in vivo and in vitro, the exact biological mechanism of garlic extract still remains unclear.
References 1 Borek, C. (2001) Antioxidant health effects of aged garlic extract. J. Nutr. 131, 1010S – 1015S
Update
TRENDS in Pharmacological Sciences
2 Qi, R. (2000) Inhibition by diallyl trisulfide, a garlic component, of intracellular Ca2þ mobilization without affecting inositol-1,4,5trisphosphophate (IP3) formation in activated platelets. Biochem. Pharmacol. 60, 1475 – 1483 3 Dirsch, V.M. (1998) Ajoene, a compound of garlic, induces apoptosis in human promyeloleukemic cells, accompanied by generation of reactive oxygen species and activation of nuclear factor kB. Mol. Pharmacol. 53, 402 – 407
63
Vol.24 No.2 February 2003
4 Hirsch, K. (2000) Effect of purified allicin, the major ingredient of freshly crushed garlic, on cancer cell proliferation. Nutr. Cancer 38, 254
0165-6147/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0165-6147(02)00014-7
Empirical models and Hill coefficients Jesu´s Giraldo Grup de Modelitzacio´ Estructural i Funcional de Sistemes Biolo`gics, Institut de Neurocie`ncies and Unitat de Bioestadı´stica, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
The estimation of the Hill coefficient for asymmetric concentration – effect curves is discussed. A practical definition for the calculation of the Hill coefficient at the mid-point is provided and applied to some selected empirical models. Empirical models are used to characterize E/[A] curves, where E is the pharmacological effect and [A] is the concentration of agonist, using a set of parameters that lack physical meaning. One of the most applied models in pharmacology is the Hill Equation [1], which in a semilogarithmic scale can be written as: a ½Eqn 1 E¼ 1 þ 10mðxb 2xÞ where x ¼ log½A; and the parameters a, xb and m determine the maximum response (upper asymptote), the location (mid-point) and the steepness (slope) of the E/x curve, respectively. A known transformation of Eqn 1 is the Hill plot [2]: log
E ¼ mx 2 mxb a2E
½Eqn 2
The Hill plot is a straight line; its slope m is named the Hill coefficient and denoted nH : From this expression, the definition of the Hill coefficient can be extended to any given E/x function as: E a2E dx
dlog nH ¼
½Eqn 3
where, in contrast to the Hill equation, nH can be dependent on x. In this case and for comparative purposes, it might be convenient to calculate the Hill coefficient at the mid-point (x50: x for E ¼ a=2): 0 1 E dlog B a2E C C nH50 ¼ B ½Eqn 4 @ A dx x50
The definition of the Hill coefficient can be rearranged to Corresponding author: Jesu´s Giraldo ([email protected]). http://tips.trends.com
give: E a dE a2E ¼ £ ða 2 EÞEln10 dx dx
dlog nH ¼
which, at the mid-point, becomes [3,4]: dE 4 dx x50 nH50 ¼ aln10
½Eqn 5
½Eqn 6
Equations 4 and 6 for the calculation of nH50 are mathematically equivalent. However, Eqn 6 is apparently simpler in as much as the derivative is taken directly on E/x whereas a logarithmic transformation is needed for Eqn 4. In addition, Eqn 6 makes it clear that nH50 is a normalized expression of the slope (first derivative) of the E/x curve at the mid-point, and, consequently, a measure of the sensitivity of the pharmacological system to small changes in agonist concentration. The Hill equation is inherently symmetric: the midpoint matches the point of inflection (the point on the curve at which the curvature changes from convex to concave or vice versa). This property constrains the flexibility of the model for curve fitting. In this regard, it was found from experiments with a1-adrenoceptor agonists in rat aorta that models allowing for asymmetry provided a significantly better fit of the data than the Hill model, which implies that the experimental E/x curves were asymmetric [5]. This issue was addressed in a recent study in which the contractile response of rat vas deferens to noradrenaline in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) was compared. Results showed that SHRs produced symmetric curves whereas those from WKY rats were asymmetric [4]. It seems logical to infer that if the data require an empirical E/x model different from the Hill equation, the appropriate expression for the Hill coefficient is obtained by applying Eqns 4 or 6 to the chosen model. Table 1 shows the E/x functions together with the derived Hill coefficients for some selected empirical models. The Hill, Gompertz and Modified Hill equations are nested within the Richards model. We see that the Hill
62
TRENDS in Pharmacological Sciences
number of side-effects will merit comparison with metabolites of some of the 2700 isoforms of cytochromes P450 as a model for the drug-binding choices of these enzymes and the transiency of a receptor conformation [5]. It is generally recognized that, overall, the lowest energy conformations that are stable are, at present, largely unpredictable for proteins (including enzymes and receptors). Therefore, the existence of multiple conformations of receptors (provided by multiple domains), some of which do not affect the putative main ligand binding site, cannot be ignored both in silico and in the laboratory [3] if we are to eliminate most of the distressing side-effects produced by therapeutic, particularly neuroleptic, drugs.
Vol.24 No.2 February 2003
References 1 Kenakin, T. and Onaran, O. (2002) The ligand paradox between affinity and efficacy: can you be there and not make a difference? Trends Pharmacol. Sci. 23, 275– 280 2 Palmer, T. (2001) Enzymes: Biochemistry, Biotechnology, Clinical Chemistry, Horwood Publishing, Chichester, UK 3 Wiseman, A. and Woods, L.F.J. (2002) Can ‘real-lab’ supersede ‘virtualligand’ promises? Trends Pharmacol. Sci. 23, 261 4 Wiseman, A. et al. (2002) Are food and environmental toxicants ‘overdetected’ by bioassay? Trends Biotechnol. 20, 13 – 15 5 Wiseman, H. et al. (2000) Biomolecular Free Radical Toxicity: Causes and Prevention, John Wiley and Sons
0165-6147/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0165-6147(02)00047-0
Pharmacological effects of garlic extract Ruomei Qi1 and Zhengang Wang2 1 2
Beijing Institute of Geriatrics, Beijing Hospital Ministry of Health, No.1 Dahualu Beijing 100730, China Institute of Basic Medical Science, Beijing Union Medical College and Chinese Academy of Medical Science, Beijing, China
Garlic has been used as a herbal medicine for thousands of years. Recent studies have demonstrated that garlic contains several medically active substances that possess many favorable effects, such as a decrease in low-density lipoprotein (LDL), antioxidation, anti-thrombosis and suppression of platelet aggregation. In recent years, it has become apparent that an increasing number of people prefer to take natural medicines rather than chemical synthetics. Thus, research into natural garlic extract has attracted greater attention. Oxidative modification of DNA is related to aging and diseases such as cardiovascular diseases, neurodegenerative diseases and even cancer. Garlic extract exhibits antioxidant action by increasing the levels of cellular antioxidant enzymes, such as superoxide dismutase, catalase and glutathione peroxidase, and scavenging reactive oxygen species [1], and thus might have some benefit in diseases in which reactive oxygen species play a part. Oxidation of LDL is an important process in the development of atherosclerosis. Recent studies have demonstrated that garlic extract can inhibit LDL oxidation in vitro, reduce plasma LDL in vivo and retard atherogenesis in rabbits. It is therefore reasonable to suggest that garlic extract might be useful in the prevention of the progression of atherosclerosis in humans. Platelets play a crucial role in thrombosis and, indeed, the prevention and treatment of thrombosis is focused mainly on the inhibition of platelet function. Garlic extract has been shown to suppress platelet aggregation strongly by inhibiting intracellular Ca2þ mobilization and thromboxane A2 (TXA2) generation. TXA2 is a metabolic product of arachidonic acid and an endogenous stimulant of platelet activity. Inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3], a well known intercellular second messenger, can mediate Corresponding author: Ruomei Qi ([email protected]). http://tips.trends.com
Ca2þ release following activation of phospholipase C by certain agonists. Garlic extract, however, exerts its action through neither the inhibition of the generation of Ins(1,4,5)P3 nor Ca2þ-depletion-induced Ca2þ influx, but by the inhibition of Ca2þ mobilization. It therefore proposed that garlic extract might act downstream of Ins(1,4,5)P3 [2]. Ajoene, a garlic-derived natural compound, has been shown to induce apoptosis in leukemic cells in addition to other blood cells of leukemic patients. Ajoene induces apoptosis in human leukemic cells via stimulation of peroxide production and activation of nuclear factor kB. This new biological effect might elucidate the molecular mechanism of the anti-tumor action of ajoene [3]. Ajoene also affects apoptosis by activation of caspase-3-like activity and caspase-8 activity in leukemic cell lines. Another study demonstrated that purified allicin (another major compound of garlic extract) inhibited proliferation of human mammary (MCE-7) endometrial and colon (HT-29) cancer cells. The inhibition of growth was accompanied by an accumulation of the cell in G0/G1 and G2/M phase of the cell cycle and not by a significant increase in cell death. This result implies that allicin is responsible for the antiproliferative effect of garlic extract [4]. Taken together, the beneficial effects of garlic extract make it useful in health care. Many countries have used garlic extract for clinical treatments, but the untoward actions of garlic extract following long-term administration should be fully noted. Even though many studies on garlic extract have been performed in vivo and in vitro, the exact biological mechanism of garlic extract still remains unclear.
References 1 Borek, C. (2001) Antioxidant health effects of aged garlic extract. J. Nutr. 131, 1010S – 1015S
Update
TRENDS in Pharmacological Sciences
2 Qi, R. (2000) Inhibition by diallyl trisulfide, a garlic component, of intracellular Ca2þ mobilization without affecting inositol-1,4,5trisphosphophate (IP3) formation in activated platelets. Biochem. Pharmacol. 60, 1475 – 1483 3 Dirsch, V.M. (1998) Ajoene, a compound of garlic, induces apoptosis in human promyeloleukemic cells, accompanied by generation of reactive oxygen species and activation of nuclear factor kB. Mol. Pharmacol. 53, 402 – 407
63
Vol.24 No.2 February 2003
4 Hirsch, K. (2000) Effect of purified allicin, the major ingredient of freshly crushed garlic, on cancer cell proliferation. Nutr. Cancer 38, 254
0165-6147/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0165-6147(02)00014-7
Empirical models and Hill coefficients Jesu´s Giraldo Grup de Modelitzacio´ Estructural i Funcional de Sistemes Biolo`gics, Institut de Neurocie`ncies and Unitat de Bioestadı´stica, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
The estimation of the Hill coefficient for asymmetric concentration – effect curves is discussed. A practical definition for the calculation of the Hill coefficient at the mid-point is provided and applied to some selected empirical models. Empirical models are used to characterize E/[A] curves, where E is the pharmacological effect and [A] is the concentration of agonist, using a set of parameters that lack physical meaning. One of the most applied models in pharmacology is the Hill Equation [1], which in a semilogarithmic scale can be written as: a ½Eqn 1 E¼ 1 þ 10mðxb 2xÞ where x ¼ log½A; and the parameters a, xb and m determine the maximum response (upper asymptote), the location (mid-point) and the steepness (slope) of the E/x curve, respectively. A known transformation of Eqn 1 is the Hill plot [2]: log
E ¼ mx 2 mxb a2E
½Eqn 2
The Hill plot is a straight line; its slope m is named the Hill coefficient and denoted nH : From this expression, the definition of the Hill coefficient can be extended to any given E/x function as: E a2E dx
dlog nH ¼
½Eqn 3
where, in contrast to the Hill equation, nH can be dependent on x. In this case and for comparative purposes, it might be convenient to calculate the Hill coefficient at the mid-point (x50: x for E ¼ a=2): 0 1 E dlog B a2E C C nH50 ¼ B ½Eqn 4 @ A dx x50
The definition of the Hill coefficient can be rearranged to Corresponding author: Jesu´s Giraldo ([email protected]). http://tips.trends.com
give: E a dE a2E ¼ £ ða 2 EÞEln10 dx dx
dlog nH ¼
which, at the mid-point, becomes [3,4]: dE 4 dx x50 nH50 ¼ aln10
½Eqn 5
½Eqn 6
Equations 4 and 6 for the calculation of nH50 are mathematically equivalent. However, Eqn 6 is apparently simpler in as much as the derivative is taken directly on E/x whereas a logarithmic transformation is needed for Eqn 4. In addition, Eqn 6 makes it clear that nH50 is a normalized expression of the slope (first derivative) of the E/x curve at the mid-point, and, consequently, a measure of the sensitivity of the pharmacological system to small changes in agonist concentration. The Hill equation is inherently symmetric: the midpoint matches the point of inflection (the point on the curve at which the curvature changes from convex to concave or vice versa). This property constrains the flexibility of the model for curve fitting. In this regard, it was found from experiments with a1-adrenoceptor agonists in rat aorta that models allowing for asymmetry provided a significantly better fit of the data than the Hill model, which implies that the experimental E/x curves were asymmetric [5]. This issue was addressed in a recent study in which the contractile response of rat vas deferens to noradrenaline in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) was compared. Results showed that SHRs produced symmetric curves whereas those from WKY rats were asymmetric [4]. It seems logical to infer that if the data require an empirical E/x model different from the Hill equation, the appropriate expression for the Hill coefficient is obtained by applying Eqns 4 or 6 to the chosen model. Table 1 shows the E/x functions together with the derived Hill coefficients for some selected empirical models. The Hill, Gompertz and Modified Hill equations are nested within the Richards model. We see that the Hill