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27 Cards in this Set
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Glycosides chemistry 4
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• Are molecules which consist of a sugar moiety attached to one or more non-sugar moiety (portion).
• They are hydrolysed by enzymes or acids into a glycone (sugar) and an aglycone - the active portion, which may be a phenol, alcohol or sulphur compound. • Many are toxic in overdose - especially cyanogenic and cardiac glycosides, but cooking generally inactivates them. • Most glycosides can be classed as ‘prodrugs’ since they remain inactive until they are hydrolised in the large bowel with the help of specialised bacteria, leading to the release of the aglycone |
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Types of Glycosides 4
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• Cardioactive glycosides
• Cyanogenic glycosides • Glucosinolates • Anthraquinones glycosides – Phenols |
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Cardioactive Glycosides Properties Pengally 5
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• Increase the force and speed of the systolic contraction
• In a failing heart they cause a more complete emptying of the ventricles and shortening the length in systole • The heart has more time to rest between contractions • Increased cardiac output causes a lower heart rate and increase excretion from the kidneys • They have a complex sugar moiety which effects the bioavailability and distribution of the aglycone, and its specific presentation to the cardiac tissue |
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Cardioactive Glycosides Contraindications
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• CAG’s have a low therapeutic index (0.5) meaning the therapeutic dose is not much lower than the toxic dose
• They should be administered with care and with close observation • They have a complex sugar moiety which effects the bioavailability and distribution of the aglycone, and its specific presentation to the cardiac tissue • Since potassium and CAGs arte antagonistic in function a lack of potassium will lead to toxicity effects such as arrhythmias, bradycardia and nausea and vomiting due to direct stimulation of the chemoreceptor trigger zone in the medulla • Diuretics are often part of the treatment of heart failure and therefore potassium supplementation is essential to make up the loss from the kidneys. |
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Cardioactive Glycoside Families 3
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• Liliaceae – Convallaria majalis
• Scrophulariaceae – Digitalis purpurea, Digitalis lanata • Aponcynaceae – Strophanthus gratus - Rose Allamanda |
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CAG’s Actions and treatment protocols
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• The effects on the vagus make digitalis CAGs a valuable therapeutic tool for the treatment of atrial arrhythmias.
• The effect of CAGs on healthy heart tissue will be minimal. • A minimal level of potassium is needed to regulate the action of CAGs (consider a potassium rich diet including bananas, tomatoes etc., or include Taraxacum officinale fol. in the prescription. • Since potassium and CAGs are antagonistic in function a lack of potassium will lead to toxicity effects such as arrhythmias, bradycardia and nausea and vomiting due to direct stimulation of the chemoreceptor trigger zone in the medulla. • Diuretics are often part of the treatment of heart failure and therefore potassium supplementation is essential to make up the loss from the kidneys. |
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CAG found in Digitalis purpurea
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Digitoxin, gitoxin
Scrophulariaceae |
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CAG found in Digitalis lantana
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Lanatosides A - E, Digoxin
Scrophulariaceae |
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CAG found in Convallaria majalis
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Convallotoxin with rhamnose, Convalloside with rhamnose and glucose
Liliaceae |
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Cyanogenic Glycosides general 3
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• Hydrolysis of these molecules leads to the formation of hydrogen cyanide/ prussic acid
• Highly toxic in quantity • Are found in more the 800 species in 80 plant families, including some therapeutically valuable plants |
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Toxicology Pen
Toxicity of hydrocyanic acid causes: 3 |
• Inactivation of the respiratory enzymes, leading to dizziness and high facial colour
• High doses, the whole CNS ceases to function and causes death • In small doses our bodies are able to neutralize cyanides by converting them to thiocyantes, which are eliminated in the urine. |
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Cyanogenic Glycosides Examples 5
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• Amygdalin/ laetrile, B17 Prunus amygdalus (Almond)and other Roseaceae species
• Prunasin Prunus padus/serotina (Wild cherry) and other species including plums • Sambunigrin Sambucus nigra • Linamarin - Linum usitatissimum,Trifolium repens • Lotaustralin Trifolium repens(white clover), Lotus spp. |
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Cyanogenic Glycosides Actions
In small amounts cyanogenic glycosides are: |
• Antispasmodic
• Sedative • Increase vagal tone on the heart, and thus slow the pulse and lower the blood pressure • Increase vagal tone on digestive system which improves digestion (hence almonds and almond desserts at the end of a meal). • Anaesthetic • Excreted rapidly mainly via the lungs, giving the effect of transiently increasing respiration |
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Cyanogenic Glycosides Herbal Actions
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• Antispasmodic, Sedative, Hypotensive, Stomatic, Anaesthetic
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Amygdalin/ laetrile
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Prunus amygdalus (Almond)and other Roseaceae species
Cyanogenic glycoside |
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Prunasin
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Prunus padus/serotina (Wild cherry) and other species including plums
Cyanogenic glycoside |
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Sambunigrin
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Sambucus nigra
Cyanogenic glycoside |
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Linamarin
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Linum usitatissimum, Trifolium repens
Cyanogenic glycoside |
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Glucosilinates glycosides – Mustard, cabbage, rocket general & contras
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• Mainly found in the Brassicaceae family
• There are more than 100 glucosilinates which are produced as a defense by the plant • When the plant is attacked an enzyme called myrosinase is released which hydrolyses the glucosilinate to glucose and the aglycone • When the plants are bruised the compounds are hydrolysed by thioglucosidase. This relases an unstable aglycone which is converted to isothiocyanate • These compounds are pungent smelling and tasting and irritate the skin and the mucous membrane lining the GIT. • They can also cause kidney and liver damage • They can inhibit the uptake of iodine by the thyroid • However, the small amounts consumed in brassicas in the human diet should not be enough to cause toxicity or thyroid problems. |
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Glucosilinates glycosides Actions 8
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• Topical application causes vasodilation, they have a rubefacient effect. Hence the use of mustard poultices to break up congestion in the lungs and bronchioles (care must be taken not to blister the skin).
• When preparing a poultice warm water should be used to aid hydrolysis but it should be no more than 45’C as a preponderance of toxic nitriles will then be formed. • Internally they are decongestants for sinus conditions due to the isothiocyanates. • Absorption and excretion into the lungs helps to break down bronchial catarrh. • They stimulate digestion, but large doses can cause emesis. • They are antibiotic and immuno-stimulant. • Dietary intake of gluycosilinates may protect against colon cancer • They made be used therapeutically in the treatment of hyperthyroidism. The milk from cows feeding on a diet high in brassicas apparently has the same effect. |
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Glucosilinates glycosides Examples 7
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• Sinalbin Sinapsis alba White mustard, Brassica napus Rapeseed
• Sinigrin Brassica nigra,/ napus, Raphanus sativus Radish, Capsella bursa-pastoris, Amoracia rusticana.Horseradish • Glucoputranjivin Amoracia rusticana, Raphanus sativus, Cochlearia officinalis - scurvygrass • Glucoraphenin Raphanus sativus, Plantago major • Gluconasturtiin Masturtium officinale, Brassica rapa/napus/nigra Mustard, Sinapsis alba, Amoracia rusticana. • Glucotropaeolin Trapaeolum majus, Reseda lutea • Glucoibervirin Cheiranthus cheiri, Brassica napus. |
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Glucosilinates Contraindications 4
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1. They stimulate digestion, but large doses can cause emesis.
2. These compounds are pungent smelling and tasting and irritate the skin and the mucous membrane lining the GIT. 3. They can also cause kidney and liver damage 4. They can inhibit the uptake of iodine by the thyroid |
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How Cardioactive Glycosides work
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• They compete with the potassium/calcium sites in the myocardium
• So that potassium is lost from the cells and the action of calcium in potentiating muscle contraction is encouraged. • ATPase bound to the cell membrane is significantly inhibited • This gives rise to general inhibition of the active ionic transport so sodium accumulates in the cell and potassium is lost. • These actions cause inotropic and chrontropic effects • Increase the efficiency of the heart stroke • Decrease the heart rate • Decrease the demand if oxygen needed by the heart. • Need a min amount of potassium to regulate their effect |
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Glucosilinates Contraindications
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1. They stimulate digestion, but large doses can cause emesis.
2. These compounds are pungent smelling and tasting and irritate the skin and the mucous membrane lining the GIT. 3. They can also cause kidney and liver damage 4. They can inhibit the uptake of iodine by the thyroid |
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Sinigrin
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Glucosilinates found in Brassica nigra,/ napus, Raphanus sativus - Radish, Capsella bursa-pastoris, Amoracia rusticana.Horseradish
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Gluconasturtiin
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Glucosilinates found in Brassica rapa/napus/nigra Mustard, Sinapsis alba, Amoracia rusticana.
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Glucoraphenin
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Glucosilinates found in
Raphanus sativus - radish, Plantago major |
