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Rottlerin
Chemical compound From Wikipedia, the free encyclopedia
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Rottlerin (mallotoxin) is a polyphenol natural product isolated from the Asian tree Mallotus philippensis. Rottlerin displays a complex spectrum of pharmacology.[1]
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Effects
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Perspective
Uncoupler of oxidative phosphorylation
Rottlerin has been shown to be an uncoupler of mitochondrial oxidative phosphorylation.[2][3][4]
Potassium channel opener
Rottlerin is a potent large conductance potassium channel (BKCa++) opener.[5] BKCa++ is found in the inner mitochondrial membrane of cardiomyocytes.[6] Opening these channels is beneficial for post-ischemic changes in vasodilation.[7] Other BKCa++ channel openers are reported to limit the mitochondrial calcium overload due to ischemia.[8][9] Rottlerin is also capable of reducing oxygen radical formation.[1]
Other BKCa++ channel openers (NS1619, NS11021 and DiCl-DHAA) have been reported to have cardio-protective effects after ischemic-reperfusion injury.[9][10][11] There were reductions in mitochondrial Ca++ overload, mitochondrial depolarization, increased cell viability and improved function in the whole heart.[9][10][11]
Mallotoxin is also a hERG potassium channel activator.[12]
Role in cardioplegia reperfusion
Clements et al.[5] reported that rottlerin improves the recovery of isolated rat hearts perfused with buffer after cold cardioplegic arrest. A majority of patients recover but some develop a cardiac low-output syndrome attributable in part to depressed left ventricular or atrial contractility, which increases chance of death.[5]
Contractility and vascular effects
Rottlerin increases in isolated heart contractility independent of its vascular effects, as well as enhanced perfusion through vasomotor activity.[5] The activation of BKCa++ channels by rottlerin relaxes coronary smooth muscle and improves myocardial perfusion after cardioplegia.[5]
Myocardial stunning is associated with oxidant radical damage and calcium overload.[5] Contractile abnormalities can occur through oxidant-dependent damage and also through calcium overload in the mitochondria resulting in mitochondrial damage.[13][14][15] BKCa++ channels reside in the inner mitochondrial membrane[6] and their activation is proposed to increase K+ accumulation in mitochondria.[8][9] This limits Ca2+
influx into mitochondria, reducing mitochondrial depolarization and permeability transition pore opening.[8][9] This may result in less mitochondrial damage and therefore greater contractility since there is a decrease in apoptosis compared to no stimulation of BKCa++ channels.[5]
Akt activation
Rottlerin also enhances the cardioplegia-induced phosphorylation of Akt on the activation residue Thr308.[5] Akt activation modulates mitochondrial depolarization and the permeability transition pore.[16][17] Clements et al.[5] found that Akt functions downstream of the BKCa++ channels and its activation is considered beneficial after ischemic-reperfusion injury. It is unclear what the specific role of Akt may play in modulating of myocardial function after rottlerin treatment of cardioplegia.[5] More research needs to be done to examine if Akt is necessary to improve cardiac function when rottlerin is administered.[5]
Antioxidant properties
The antioxidant properties of rottlerin have been demonstrated but it is unclear whether the effects are because of BKCa++ channel opening or an additional mechanism of rottlerin.[1][5][18] There was no oxygen dependent damage found by rottlerin in the study conducted by Clements et al.[5]
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Ineffective PKCδ selective inhibitor
Rottlerin has been reported to be a PKCδ inhibitor.[19] PKCδ has been implicated in depressing cardiac function and cell death after ischemia-reperfusion injury as well as promoting vascular smooth muscle contraction and decreasing perfusion.[5] However, the role of rottlerin as a specific PKCδ inhibitor has been questioned. There have been several studies using rottlerin as a PKCδ selective inhibitor based on in vitro studies, but some studies showed it did not block PKCδ activity and did block other kinase and non-kinase proteins in vitro.[1][20][21] Rottlerin also uncouples mitochondria at high doses and results in depolarization of the mitochondrial membrane potential.[1] It was found to reduce ATP levels, activate 5'-AMP-activated protein kinase and affect mitochondrial production of reactive oxygen species (ROS).[1][6][22] It is difficult to say that rottlerin is a selective inhibitor of PKCδ since there are biological and biochemical processes that are PKCδ –independent that may affect outcomes.[1][5][6][22] A proposed mechanism of why rottlerin was found to inhibit PKCδ is that it decreased ATP levels and can block PKCδ tyrosine phosphorylation and activation.[1]
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Sources
The Kamala tree, also known as Mallotus philippensis, grows in Southeast Asia.[19] The fruit of this tree is covered with a red powder called kamala, and is used locally to make dye for textiles, syrup and used as an old remedy for tape-worm, because it has a laxative effect.[23] Other uses include afflictions with the skin, eye diseases, bronchitis, abdominal disease, and spleen enlargement but scientific evidence is not present.[24]
References
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