Colchicine (C 22 H 25 NO 6) is a neutral lipophilic tricyclic alkaloid with weak anti-inflammatory activity. It is extracted from two plants: Colchicum autumnale (autumn crocus, meadow saffron) and Gloriosa superba (glory lily).
Colchicum autumnale: commonly known as autumn crocus, meadow saffron or naked lady, is a flower that resembles the true crocuses, but blooms in autumn. (This is not a reliable distinction, however, since many true crocuses flower in autumn.) The name "naked lady" comes from the fact that the flowers emerge from the ground long after the leaves have died back.
The species is commonly cultivated in temperate areas.
The bulb-like corms of Colchicum autumnale contain colchicine, a useful drug with a narrow therapeutic index.
Colchicum plants have been mistaken by foragers for Ramsons, which they vaguely resemble, but are deadly poisonous due to their colchicine content. The symptoms of colchicine poisoning resemble those of arsenic, and no antidote is known.
Colchicine has anti-inflammatory, anti-mitotic, and anti-fibrotic activity. It is used in the treatment of autoinflammatory diseases and acute gout. It, infact, inhibits uric acid crystal deposition, which is enhanced by a low pH in the tissues, probably by inhibiting oxidation of glucose and subsequent lactic acid reduction in leukocytes. Colchicine also finds applications in various other diseases like pseudogout, familial Mediterrenian fever, cirrhosis of the liver and bile, pericarditis, and amyloidosis.
The pharmacotherapeutic mechanisms of action in diverse disorders is not fully understood, thought is known that the drug accumulates preferentially in neutrophils.
Colchicine modulates the production of chemokines and prostanoids, inhibits neutrophil and endothelial cell adhesion molecules and eventually it decreases neutrophil degranulation, chemotaxis and phagocytosis, thus reducing the initiation and amplification of inflammation. Recently, colchicine is used as a selective neurotoxin in animal models to study Alzheimer’s dementia.
In genetic experiments on plants, colchicine is widely used to separate chromosomes at the metaphase and to induce polyploidy.
Mechanism of inhibition of microtubule assembly dynamics by Colchicine
Colchicine interacts with tubulin and perturbs the assembly dynamics of microtubules. Microtubules, the key components of cytoskeleton are made up of a,b-tubulin heterodimers. In eukaryotic cells, they organize to form stable interphase microtubule network and highly dynamic mitotic spindle. Microtubules are involved in a variety of cellular processes such as cell division, maintenance of cell shape, cell signalling, cell migration, and cellular transport.
Suppression of microtubule dynamics in cells by small molecule inhibitors, as Colchicine, blocks the cell division machinery at mitosis leading to cell death. Therefore, the assembly dynamics of microtubule represents a potential target for finding anti-cancer drugs. The small molecule inhibitors may imitate the action of the natural regulators of microtubule assembly and disassembly kinetics making these agents a valuable tool for probing the roles of microtubule dynamics in different cellular processes.
Microtubule-targeted agents can be broadly divided into two groups, namely polymerization inhibitors and polymerization promoters. Several natural and synthetic compounds of varied structures such as vinca alkaloids , colchicine, estramustine, and combretastatins inhibit microtubule polymerization whereas compounds such as taxanes , laulimalides, and discodermolides promote microtubule assembly. The binding sites of taxol, colchicines, and vinblastine in tubulin are well characterized. Taxol and vinblastine bind to the b-subunit whereas colchicine binds at the interphase of a and b subunits of the tubulin heterodimer.
Colchicine blocks cell division by distrupting microtubules and the spindle microtubules are more sensitive to colchicine than the interphase microtubules. Colchicine penetrates the cells and equilibrates with the external colchicine rapidly, however a longer period is required to attain saturation. The binding of colchicine to microtubules dissociates them into tubulin dimers. Cells in different stages of mitosis exhibit differential sensitivity to colchicine. At higher concentrations, cells at metaphase were blocked immediately after the addition of colchicine. At lower concentrations, the prophase cells were more sensitive and were blocked while those in metaphase and anaphase completed mitosis. Colchicine at a concentration of 50nM blocks almost all the cells at mitosis. The cells blocked at mitosis undergo abnormal mitotic cycle, designated as or . C-mitosis is characterized by partial or complete absence of spindle apparatus following the breakdown of nuclear envelope, condensed chromosomes, and undivided centromeres. Several studies have shown that colchicine can inhibit the function of several ion channels and the depolymerizing effect of the drug is hypothesized to be involved in this effect. Colchicine was shown to alter the membrane potential of the mitochondria resulting in the release of proapoptotic factors like caspases, cytochrome-c, and apoptosis-inducing factors, leading to apoptotic cell death.
Tubuline works like a receptor for colchicine; in its structure, a and b tubulin possess identical principal structure: each monomer being composed of a core of two beta sheets surrounded by a helices. The monomer has compact structure, which can be divided into three functional domains: the amino-terminal domain possessing the nucleotide-binding region, an intermediate domain where lies the Taxol-binding site, and the carboxyl-terminal domain comprising the binding site for motor proteins. Each monomer was composed of parallel b-strands alternating with helices. There is a direct involvement of the loops, which connects each strand with the start of the next helix.
The crystal structure of animal tubulin-colchicine complex
Colchicine does not bind to microtubules unless it first forms a , which adds to the microtubule ends. Microtubule polymerization is inhibited by substoichiometric concentrations of colchicine implying that it inhibits tubulin polymerization by binding to the ends of micro-tubules rather than to the soluble tubulin.
Microtubules in a protofilament are stabilized through both lateral and longitudinal interactions. The loop defined "M loop" is the central element of the interactions. It protrudes out from one side of the protofilament and makes intimate contact with several other loops. So any effect on the adjoining loops gets transmitted to the M loop and consequently the microtubule becomes destabilized. The colchicine site in the tubulin-colchicine crystal structure lies within the
intermediate domain of the b subunit. At low TC-complex concentration, the complex incorporates into microtubule disturbing formation of lateral contacts at the newly formed end of protofilaments because of displacement of the M loop resulting from entry of colchicine.
Colchicine-site agent as anti-cancer drugs
There are several therapeutically important drugs that bind to the colchicine-binding site of tubulin. An example are Indole sulfonamides:
Inhibite HeLa cell proliferation and block cell cycle progression at mitosis by depolymerizing cellular microtubules and disorganizing chromosomes. They also inhibit the microtubule formation in vitro and at low concentrations, suppress the dynamic instability behaviour at plus ends of individual steady state microtubules in vitro. The indole sulfonamides perturb the assembly dynamics of spindle microtubules that arrest the cell proliferation at mitosis. The mitotically arrest cells eventually underwent apoptotic cell death mediated by the bcl-2 pathway.
Use of Colchicine for the treatment of Gout
Gout is a common arthritis due to the deposition of monosodium urate (MSU) crystals within joints, following chronic hyperuricemia. It affects 1-2% of adults in Western countries, where it is the most common inflammatory arthritis in men. Epidemiologic data are consistent with an increase in the prevalence of gout.
Acute gouty arthritis most commonly begins with the involvement of a single joint in the lower ex-tremities (85 – 90% of cases), often the first metatarsophalangeal joint. The standard pharmacological management of acute attacks of gout involves use of oral colchicine or non-steroidal anti-inflammatory drugs (NSAIDs) or corticosteroids. NSAIDs are more commonly used in the USA and northern Europe, and colchicine in France and some countries of southern Europe. Colchicine is also used as a prophylactic treatment to prevent flares after the initiation of urate-lowering therapy (ULT). Indeed, gouty attacks may be induced by the rapid reduction in urate levels that follows the initiation of ULT. One strategy to prevent or to reduce the frequency of acute attacks is to give low-dose colchicine a few weeks before ULT, and to continue it as long as tophi are present or at least 3–6 months in the absence of tophus.
Mechanisms, mediators of crystal-induced inflammation and main sites of action of colchicine.
Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) microcrystals engage Toll-like receptor TLR2 and TLR4 on resident tissue monocytes/ macrophages. In the presence of the cyto-solic adaptor protein myeloid differentiation factor ( MyD88 ), the crystals induce the NACHT-LRR-PYD-containing protein-3 (NALP3) inflammasome, caspase-1 activation, interleukin (IL)-1β processing, and therelease of IL-1β and other cytokines (eg, tumor necrosis factor [TNF]- α , IL-6) and chemokines (eg, keratinocyte-derived cytokine [KC], IL-8, growth-related oncogene [GRO]- α ). The IL-1β and TNF-α released from the resident tissue cells stimulate endothelial cell adhesion molecules (eg, E-selectin) and neutrophil influx. Neutrophil recruitment is amplified ed by crystal induced release of S100A8/9, and neutrophil phagocytosis of the microcrystals is followed by release of IL-1 β , IL-8, superoxide anions, and prostaglandin E2 (PGE2).
At , colchicine suppresses MSU crystal-induced, NALP3 inflammasome-driven caspase-1 activation and IL-1 β processing and release.
At , colchicine blocks the release of a crystal-derived chemotactic factor from neutrophil lysosomes, blocks neutrophil adhesion to endothelium by modulating the distribution of adhesion molecules on the endothelial cells, and inhibits MSU crystal-induced production of superoxide anions from neutrophils.
The pharmacokinetics and pharmacodynamics of colchicine are heavily determined by its interaction and binding to three proteins:
- Cytochrome P450 3A4 ;
- Multidrug transporter P-glycoprotein .
Example of commercial drug: Colcrys™
•Prophylaxs of Gout Flares
•Treatment of Gout Flares
•Familial Mediterranean fever (FMF)
•More common side effects:
•Nausea or vomiting
•Prophylaxis of Gout flares:
The recommended dosage of COLCRYS for prophylaxis of gout flares for adults and adolescents older than 16 years of age is 0.6 mg once or twice daily. The maximum recommended dose for prophylaxis of gout flares is 1.2 mg/day.
•Treatment of Gout Flares:
The recommended dose of COLCRYS for treatment of a gout flare is 1.2 mg (2 tablets) at the first sign of the flare followed by 0.6 mg (1 tablet) one hour later. Higher doses have not been found to be more effective. The maximum recommended dose for treatment of gout flares is 1.8 mg over a 1 hour period. COLCRYS may be administered for treatment of a gout flare during prophylaxis at doses not to exceed 1.2 mg (2 tablets) at the first sign of the flare followed by 0.6 mg (1 tablet) one hour later. Wait 12 hours and then resume the prophylactic dose.
•COLCRYS (colchicine) is a substrate of the efflux transporter P-glycoprotein (P-gp). Of the cytochrome P450 enzymes tested, CYP3A4 was mainly involved in the metabolism of colchicine. If COLCRYS is administered with drugs that inhibit P-gp, most of which also inhibit CYP3A4, increased concentrations of colchicine are likely. Fatal drug interactions have been reported.
•Physicians should ensure that patients are suitable candidates for treatment with COLCRYS and remain alert for signs and symptoms of toxicities related to increased colchicine exposure as a result of a drug interaction. Signs and symptoms of COLCRYS toxicity should be evaluated promptly and, if toxicity is suspected, COLCRYS should be dis-continued immediately.
Examples of drugs with potential to cause colchicine accumulation, increased pharmacologic effects, and toxicity