Definition of Steroids:
Steroids are a class of organic compounds characterized by a core structure of 17 carbon atoms arranged in four fused rings: three cyclohexane rings (A, B, and C) and one cyclopentane ring (D). This core structure, known as the “steroid nucleus” or “cyclopentanoperhydrophenanthrene ring system,” serves as the foundation for a wide variety of biologically active molecules, including hormones, alkaloids, and vitamins. Steroids can be classified based on their functional groups and oxidation state, such as sterols, glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens.
Biosynthesis:
Steroids are synthesized from acetyl-CoA via the mevalonate pathway. The key intermediate in steroid biosynthesis is cholesterol, which is converted into various steroids by enzymes that add or modify functional groups.
Functions:
– Hormonal Regulation: Many steroids serve as hormones (e.g., cortisol, estrogen, testosterone) that regulate various physiological processes, including metabolism, immune response, and reproduction.
– Membrane Structure: Cholesterol, a type of steroid, is an essential component of cell membranes, maintaining fluidity and structural integrity.
– Bile Acid Formation: Steroids are precursors to bile acids, which aid in fat digestion and absorption in the small intestine.
– Anti-inflammatory Activity: Some steroids, like glucocorticoids, have potent anti-inflammatory and immunosuppressive effects.
Definition of Cardiac Glycosides:
Cardiac glycosides are a group of naturally occurring compounds that exert a potent effect on the heart muscle. These compounds consist of a steroid nucleus with a lactone ring (unsaturated five- or six-membered ring) at the C-17 position and one or more sugar moieties attached to the C-3 position of the steroid nucleus. The sugars (glycones) and the non-sugar (aglycone or genin) parts are collectively known as glycosides. Cardiac glycosides are primarily found in certain plants, such as foxglove (Digitalis purpurea), oleander (Nerium oleander), and lily of the valley (Convallaria majalis).
Biosynthesis:
Cardiac glycosides are synthesized in plants through the mevalonate pathway, which produces cholesterol as an intermediate. Modifications to the steroid backbone and the addition of a lactone ring lead to the formation of different cardiac glycosides.
Functions:
– Cardiotonic Effect: Cardiac glycosides increase the force of contraction (positive inotropic effect) of the heart muscle by inhibiting the Na+/K+ ATPase pump, which leads to an increase in intracellular calcium concentration.
– Therapeutic Use: They are used in the treatment of congestive heart failure and certain types of arrhythmias (e.g., atrial fibrillation).
– Regulation of Heart Rate: Cardiac glycosides can slow down the heart rate (negative chronotropic effect) by enhancing vagal tone and reducing sympathetic activity.
Definition of Triterpenoids:
Triterpenoids are a large and diverse class of naturally occurring organic compounds that consist of six isoprene units, resulting in a 30-carbon skeleton (C30). These compounds are derived from the acyclic precursor squalene, which undergoes cyclization and subsequent modifications, such as oxidation, reduction, and glycosylation, to produce various triterpenoids. They are widely distributed in the plant kingdom and are found in fungi, marine organisms, and some insects.
Biosynthesis:
Triterpenoids are synthesized through the mevalonate pathway or the methylerythritol phosphate (MEP) pathway. The key intermediate, squalene, is cyclized by enzymes like oxidosqualene cyclase to produce different triterpenoid skeletons, such as lanosterol, which serves as a precursor for sterols, or oleanane, ursane, and lupane types of triterpenoids.
Functions:
– Structural Roles: Serve as precursors for sterols, which are essential components of cell membranes.
– Defense Mechanisms: Possess antimicrobial, antifungal, and antiparasitic properties, helping plants and other organisms defend against pathogens.
– Medicinal Properties: Many triterpenoids exhibit anti-inflammatory, anticancer, antioxidant, hepatoprotective, and immunomodulatory activities.
– Hormonal Activity: Some triterpenoids function as plant hormones (e.g., brassinosteroids) that regulate growth and development.
 Summary:
– Steroids are characterized by a four-ring core structure and have various physiological roles, including hormonal regulation, membrane structure, and anti-inflammatory effects.
– Cardiac Glycosides are steroid derivatives with potent cardiotonic properties, used mainly in heart failure treatment.
– Triterpenoids are a diverse group of 30-carbon compounds derived from squalene, with roles in plant defense and human health due to their various bioactive properties.
These three groups of compounds are fundamental to both plant and animal physiology and hold significant therapeutic potential due to their diverse biological activities.
