Colchicine Accumulation Research Articles

Cluster of Differentiation-44-Targeting Prussian Blue Nanoparticles Onloaded with Colchicine for Atherosclerotic Plaque Regression in a Mice Model.

Atherosclerosis management heavily relies on the suppression of the inflammatory response of macrophages. Colchicine's potent anti-inflammatory properties make it a promising candidate for secondary prevention against cardiovascular disease. However, its high toxicity and numerous adverse effects limit its clinical use. To address this, there is an urgent need for specific drug delivery systems to boost the level of accumulation of colchicine within atherosclerotic plaques. In this study, the cluster of differentiation-44 receptor was verified to be overexpressed in inflammatory macrophages within plaques both in vitro and in vivo. Subsequently, a Prussian blue-based nanomedical loading system with hyaluronic acid (HA) coating was constructed, and its effects were observed on the atherosclerosis regression. Colchicine and Cy5.5 were encapsulated within Prussian blue nanoparticles through self-assembly, followed by conjugation with hyaluronic acid to create col@PBNP@HA. The formulated col@PBNP@HA displayed a cubic shape and scattered distribution. Importantly, col@PBNP@HA demonstrated specific cellular uptake into lipopolysaccharide-stimulated macrophages. In vitro experiments showed that col@PBNP@HA more effectively inhibited expression of inflammatory factors and scavenged reactive oxygen species compared with the control group, which were treated with colchicine. Furthermore, col@PBNP@HA exhibited its specific and higher accumulation in aortic plaque analysis via fluorescence imaging of aortas. After 4 weeks, administration of col@PBNP@HA resulted in significant atherosclerosis regression in the mice model, with therapeutic effects superior to those of free colchicine. Similar to colchicine, col@PBNP@HA inhibited the secretion of inflammation factors and scavenged ROS through the regulation of the toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (Myd88)/nuclear factor kappa-B (NF-κB) and peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) signaling pathway. In summary, col@PBNP@HA demonstrated specific targeting ability to inflammatory plaques and exerted beneficial effects on atherosclerosis regression through TLR4/Myd88/NF-κB and PGC-1α modulation.

Colchicine (a high-priced alkaloid) accumulation and HPTLC quantification in different stages of in vitro developed tuber of Gloriosa superba L.

BackgroundGloriosa superba L. belongs to Colchicaceae, which is an important medicinal plant containing high-priced alkaloid colchicines and other potent phytochemicals. Due to its extensive importance at the industrial level, this plant is overexploited. Moreover, indiscriminate harvesting for raw material leads to a decline in the population of this plant in the natural environment. Thus, the present study deals with the optimization of colchicine accumulation from the different intervals of in vitro and in vivo tubers of Gloriosa.ResultTo obtain in vitro tuberization, shoot tip explants were inoculated on Murashige and Skoog medium prepared with 3 mg/l BA and 0.5 mg/l Kn + 1 mg/l 2, 4-D followed by 2 mg/l BA + 0.2 mg/l NAA. In the high-performance thin-layer chromatography study (HPTLC), the linearity range of colchicine was set at a concentration range of 100–1000 ng/spot with a regression value (r) of 0.99. Its Rf value (0.25) was recorded at 254 nm. The colchicine amount in the in vivo tuber was 7.75 ± 0.25% dry weight, while the nearby amount of 7.7 ± 0.40% dry weight of colchicine was produced from 2 weeks in vitro old tuber. This value was followed by the 4th-week old tuber with 6.35 ± 0.17% dry weight and then a gradual decrease in its accumulation.ConclusionThe significant results for the accumulation of colchicine at different stages were observed. Hence, this strategy of colchicine production creates a new possibility for improved production of colchicine under in vitro conditions which will be helpful to various pharmaceutical industries without damaging the plants from the natural environment.Graphical abstract

Feeding elicitors and precursors enhance colchicine accumulation in morphogenic cultures of Gloriosa superba L.

Morphogenic cultures of Gloriosa superba were initiated on Murashige and Skoog’s medium fortified with 2 mg L−1 2,4-dichlorophenoxyacetic acid (2,4-D), 0.5 mg L−1 naphthaleneacetic acid (NAA), 4% sucrose and 0.1% activated charcoal. To enhance the content of the alkaloid colchicine, morphogenic cultures were treated with different concentrations of abiotic elicitors like signalling compounds, metals, biotic elicitors, precursors and a combination of elicitors. Signalling molecules like acetyl salicylic acid (ASA) and sodium nitroprusside improved the production of colchicine. Abiotic elicitors have markedly (p ≤ 0.05 or ≤ 0.01) enhanced the colchicine content either at lower or higher concentrations. Among the metals, the highest amount of 11.67 mg of colchicine g−1 dry wt was noticed at 60 mM rubidium chloride, followed by 60 mM NaCl (11.18 mg g−1). Contrarily, in the presence of biotic elicitors such as Fusarium oxysporum, Alternaria solani, and Saccharomyces cerevisiae, colchicine content ranged only between 2 and 5.32 mg g−1, but Bacillus subtilis repressed it. Among the aromatic amino acids, phenylalanine at 500 mg L−1 influenced the highest accumulation of 19.48 mg g−1 dry tissue, followed by tryptophan (12.47 mg g−1), and tyrosine (9.87 mg g−1), a direct precursor of colchicine biosynthesis, while intact tubers and leaves contained 4.65 and 4.16 mg of colchicine g−1 dry tissue respectively. A combination of 10 µM AlCl3 and 50 µM salicylic acid (SA) registered 17.34 mg g−1 followed by 16.24 mg g−1 tissue in presence of 1 µM HgCl2 and 50 µM SA. The results suggest that the elicitor-stimulated colchicine accumulation was a stress response and can be exploited further for commercial production.

Enhanced biosynthesis of colchicine and thiocolchicoside contents in cell suspension cultures of Gloriosa superba L. exposed to ethylene inhibitor and elicitors

The present investigation reports the influence of ethylene inhibitor and elicitors on enhanced biosynthesis of colchicine and thiocolchicoside contents in cell suspension cultures of Gloriosa superba L. Elicitation is one of the approaches used for enhanced commercial production of secondary metabolites from plant cell culture system. G. superba is a rich source of colchicine and thiocolchicoside contents that are being used for the treatment of cancer. Callus was obtained from rhizomes of G. superba on MS medium containing 2.0 mg L−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.5 mg L−1 α-naphthalene acetic acid (NAA) and cell suspension cultures were initiated. The influence of elicitors [salicylic acid (SA), yeast extract (YE), and casein hydrolysate (CH)] as well as ethylene inhibitor [silver nitrate (AgNO3)] on biosynthesis of colchicine and thiocolchicoside contents was studied by exposure of cell suspension cultures with different concentrations for 15 and 30 days period. Among four elicitors tested, CH exhibited the maximum level of colchicine production [8.290 mg g−1 dry weight (DW)] at 300 mg L−1 concentration over a period of 15 days exposure, compared to the control whereas, SA at 27.624 mg L−1 concentration showed the enhanced colchicine production rate (8.149 mg g−1 DW) after 30 days exposure time when compared to non-elicited control cultures. Results show that CH and SA treated cells exhibited 8-fold higher level of colchicine biosynthesis over control. The maximum production of thiocolchicoside content in cell suspension culture obtained was 4.550 mg g−1 DW and 1.530 mg g−1 DW with 200 and 300 mg L−1 AgNO3 treatment at 15 and 30 days period, respectively. The colchicine content level was significantly increased when compare to the thiocolchicoside content in cell suspension culture. The accumulation of colchicine and thiocolchicoside contents was influenced by exposure time and doses of elicitors. Results clearly show that the elicitation experiment could enhance the biosynthesis of colchicine and thiocolchicoside contents level in cell suspension cultures of G. superba and the present protocol may be used for commercial supply of these important secondary metabolites in the future for therapeutic applications.

Saikosaponins A, C and D enhance liver-targeting effects of anticancer drugs by modulating drug transporters.

Vinegar-baked Radix Bupleuri (VBRB) is clinically used to enhance the pharmacological activity of drugs used to treat liver diseases. Our previous study demonstrated that this effect is dependent on increased drug accumulation in the liver; however, the underlying mechanism remains unclear. We hypothesize that VBRB mediated its effects by altering drug transporters. Thus, the present study was designed to determine the effects of VBRB's main components, saikosaponin A, C, and D, on drug transporters. Transporter activity was determined by measuring the intracellular concentration of transporter substrates. Protein and mRNA levels were measured by Western blot and qPCR, respectively. Colchicine was used as the substrate for P-glycoprotein (Pgp) and multidrug resistance protein (MRP) 1, cisplatin was used as the substrate for Mrp2 and organic cation transporters 2 (Oct2), and verapamil and MK571 were used as inhibitors of Pgp and MRP1, respectively. Saikosaponin A, C, and D differentially affected transporter activity. All of the saikosaponins inhibited Pgp activity in Pgp over-expressing HEK293 cells and increased substrate uptake of OCT2 in OCT2 over-expressing HEK293. Saikosaponin C and D inhibited MRP2 activity in HEK293 cells and BRL 3A cell with high MRP2 expression; saikosaponin A increased colchicine accumulation in GSH-stimulated HEK293 cells, but decreased colchicine uptake in HEK293 cells. Saikosaponin D inhibited MRP1 activity in GSH-stimulated HEK293 cells, but marginally affected the uptake of colchicine in HEK293 cells. In conclusion, saikosaponins play a role in VBRB's induced liver targeting effect through affecting drug transporters with a transporter expression amount depending manner.

Role of Exogenous Carbohydrate and Amino Acid Sources on Biomass and Colchicine Production in Nontransformed Root Cultures of Gloriosa superba

Elicitation strategies were studied for yield enhancement of colchicine, produced by root cultures of Gloriosa superba. Adventitious root cultures were established and grown in media containing 3 mg/l NAA and 1 mg/l BA. Root cultures showed variations in biomass as well as colchicine production in the presence of different exogenous carbohydrates and amino acid. Among the different sources of carbohydrates used - fructose, sucrose and dextrose gave a substantially higher biomass yield than the control. Maximum biomass was obtained in the presence of fructose. Root cultures growing in mannitol supplemented medium resulted in maximum accumulation of colchicine (0.32%). Among the amino acids, serine and phenylalanine significantly enhanced colchicine accumulation in root cultures. 0.02 mM glutamine supplemented media showed maximum (ten-fold) increase of root biomass.Plant Tissue Cult. & Biotech. 25(2): 247-256, 2015 (December)

Fab fragments of ovine antibody to colchicine enhance its clearance in the rat

Context. Colchicine is an anti-inflammatory alkaloid used for the treatment of acute gout, but has a narrow therapeutic index. Colchicine overdoses are relatively rare, but have high mortality requiring rapid treatment. Objective. To evaluate the ability of a newly available ovine fragment antigen-binding (Fab) antibody to colchicine (ColchiFab™) to protect rats against renal and other injury 24 h after colchicine ingestion. Materials and methods. Rats were gavaged with colchicine (5 mg/kg), then 2 h later injected intraperitoneally with 5 ml of sterile saline, or Fab anti-colchicine, a newly available ovine antibody to colchicine. Samples of blood were taken at 1, 2, 5 and 24 h after gavage, and urine was collected from 5 to 24 h after gavage. Concentrations of colchicine in tissue, blood and urine were measured by liquid chromatography/mass spectrometry, concentrations of Fab anti-colchicine, urinary neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 or KIM-1 by enzyme-linked immunosorbent assay or ELISA, while concentrations of creatine kinase and creatinine (Cr) were measured enzymatically. Results. Colchicine equilibrated rapidly throughout the body and increased serum creatine kinase. Fab anti-colchicine also rapidly redistributed to the blood and remained at high concentrations over 24 h. Fab anti-colchicine caused a rapid 7.1-fold increase in serum colchicine level, followed by excretion of both colchicine and Fab anti-colchicine through the urine. This was associated with the accumulation of colchicine in the kidney, a reversal of colchicine-induced diarrhoea, and increasing urinary NGAL level; from 168 ± 48 to 477 ± 255 ng/mmol Cr [mean ± standard deviation or SD]. Discussion. Fab anti-colchicine greatly increased the clearance of colchicine, although increasing NGAL level suggested the presence of mild kidney damage. Conclusion. These data suggest clinical utility for Fab anti-colchicine in the treatment of colchicine overdose.

Modulation of P-glycoprotein-Mediated Anticancer Drug Accumulation, Cytotoxicity, and ATPase Activity by Flavonoid Interactions

Flavonoids are components of plant foods and of many herbal medicines taken in combination with anticancer drugs. We have examined the potential of flavonoids to affect the accumulation and cytotoxicity of 3 cytotoxic drugs [vinblastine (VLB), daunorubicin (DNR), and colchicine (COL)] that are substrates for the ABC transporter, P-glycoprotein in a vinblastine-resistant T-cell leukemia, CEM/VBL100, that overexpresses P-glycoprotein. The effects of the flavonoids on accumulation and cytotoxicity of these drugs were different depending on the P-gp substrate used. Most of the 30 flavonoids tested decreased DNR accumulation in the VBL-resistant, but not sensitive, leukemia cells. By contrast, flavonoids that inhibited DNR accumulation enhanced the accumulation of fluorescently labeled vinblastine. None of these flavonoids affected COL accumulation. The effects of the flavonoids on the cytotoxicities of these drugs paralleled their effects on accumulation; the same flavonoids decreased DNR cytotoxicity but increased VLB cytotoxicity and had no effect on COL. Verapamil reversed the accumulation deficit and cytotoxicity of all three P-gp substrates. These effects correlated with the effects of flavonoids on P-gp-ATPase activity. Flavonoids that decreased DNR accumulation stimulated DNR-activated P-gp ATPase, whereas flavonoids that increased fluorescently labeled VLB accumulation inhibited VBL-stimulated P-gp ATPase activity, thereby accounting for the decrease or increase in cancer drug accumulation in resistant cells. We conclude that flavonoids often ingested by cancer patients may have different effects on anticancer drugs and that these findings should be considered in designing future combination treatments for cancer patients.

A Biotechnological Approach for Enhancement of Colchicine Accumulation in Iphigenia indica Kunth

An attempt has been made to enhance colchicine biosynthesis in Iphigenia indica L grown in vitro by exogenous supply of precursors and elicitors during culture. Addition of tyrosine at 30 mg l−1 enhanced colchicine accumulation up to 6.1 mg g−1 dry wt (control 0.99 mg g−1 dry wt), while 25 μM NiSO4 stimulated maximum colchicine accumulation (10.25 fold of control value). The colchicine accumulation was recorded as 16.25 mg g−1 dry wt when NiSO4 was added with tyrosine.

In vitro Microtuberization and Enhanced Colchicine Accumulation in Two Species of Gloriosa

In vitro Microtuberization and Enhanced Colchicine Accumulation in Two Species of Gloriosa

Is P-glycoprotein (ABCB1) a phase 0 or a phase 3 colchicine transporter depending on colchicine exposure conditions?

This study investigates the P-glycoprotein (Pgp)-mediated transport of its substrates in accumulation or efflux modes under steady-state conditions. The kinetics of colchicine uptake and efflux, a substrate of both Pgp and intracellular tubulin, were studied in HL60 and HL60/DNR cells; HL60/DNR cells contain 25 times more Pgp than do HL60 cells. HL60/DNR cells in a medium containing 6.25 nM colchicine, which mimics therapeutic conditions, reached steady-state twice as rapidly as did HL60 cells, and accumulated 24-times less colchicine than did HL60 cells. The Pgp inhibitor GF120918, increased colchicine uptake by HL60 cells 1.2-fold and that of HL60/DNR cells 17-fold, while it had no effect on colchicine efflux from either cell line that had been incubated with colchicine for 24 h. Colchicine kinetics fitted well a two closed-compartment model, showing that the low intracellular accumulation of colchicine in HL60/DNR cells resulted from a 11-fold decrease in colchicine uptake and a 2.3-fold increase in colchicine efflux, that could be attributed to Pgp-mediated efflux activity in HL60/DNR cells. Intracellular colchicine was mainly and similarly distributed in the cytosol in both cell lines. These data demonstrate that the kinetics of the intracellular colchicine accumulation depend on the density of Pgp and that Pgp is more a phase 0 (preventing cellular uptake) than a phase 3 (effluxing intracellular substrate) transporter under steady-state conditions, although the situation is reversed after a short incubation time (30 min), when intracellular free colchicine concentration is probably high enough for it to be removed from the cell by Pgp.

Aluminium Chloride Enhances Colchicine Production in Root Cultures of Gloriosa superba

Root cultures of Gloriosa superba were treated with 5 mM: methyl jasmonate and 125 microM: AlCl3 which enhanced the intracellular colchicine content of the roots by 50-fold and 63-fold, respectively. Ten millimolar of CaCl2 and 1 mM: CdCl2 enhanced biomass significantly (7- to 8.6-fold, respectively) while maximum release of colchicine into the medium was obtained with 10 mM: CdCl2. Casein hydrolysate, yeast extract and silver nitrate had no significant effect on growth and colchicine accumulation in root cultures.

Colchicine production in Gloriosa superba calluses by feeding precursors

Phenylalanine and tyrosine play a central role in Gloriosa superba L. calluses for the production of colchicine. The lack of biosynthetic precursors and signal inducing enzyme activity are responsible for the lower production of colchicine in vitro. B 5 medium nutrient grown calluses have a low content of colchicine, indicating that an optimal precursors level is required to increase PAL and TAL activity for colchicine accumulation. These results suggest that precursors are an important regulatory factor in colchicine accumulation in in vitro.

P-glycoprotein inhibition by glibenclamide and related compounds.

Glibenclamide is well known to interact with the sulphonylurea receptor (SUR) and has been shown more recently to inhibit the cystic fibrosis transmembrane conductance regulator protein (CFTR), both proteins that are members of the ABC [adenosine 5'-triphosphate (ATP)-binding cassette] transporters. The effect of glibenclamide and two synthetic sulphonylcyanoguanidine derivatives (dubbed BM-208 and BM-223) was examined on P-glycoprotein, the major ABC transporter responsible for multidrug resistance (MDR) in cancer cells. To this end, we employed different cell lines that do or do not express P-glycoprotein, as confirmed by Western blotting: first, a tumour cell line (VBL600) selected from a human T-cell line (CEM) derived from an acute leukaemia; second, an epithelial cell line derived from a rat colonic adenocarcinoma (CC531(mdr+)) and finally, a non tumour epithelial cell line derived from the proximal tubule of the opossum kidney (OK). Glibenclamide and the two related derivatives inhibited P-glycoprotein because firstly, they acutely increased [3H]colchicine accumulation in P-glycoprotein-expressing cell lines only; secondly BM-223 reversed the MDR phenomenon, quite similarly to verapamil, by enhancing the cytotoxicity of colchicine, taxol and vinblastine and thirdly, BM-208 and BM-223 blocked the photoaffinity-labelling of P-glycoprotein by [3H]azidopine. Furthermore, glibenclamide is itself a substrate for P-glycoprotein, since the cellular accumulation of [3H]glibenclamide was low and substantially increased by addition of P-glycoprotein substrates (e. g., vinblastine and cyclosporine) only in the P-glycoprotein-expressing cell lines. We conclude that glibenclamide and two sulphonylcyanoguanidine derivatives inhibit P-glycoprotein and that sulphonylurea drugs would appear to be general inhibitors of ABC transporters, suggesting an interaction with some conserved motif.

ATP-Dependent Colchicine Transport by Human Erythrocyte Glutathione Conjugate Transporter

We have recently demonstrated mutually inhibitory ATP-dependent transport of dinitrophenyl-S-glutathione (DNP-SG) and doxorubicin by DNP-SG ATPase purified from human erythrocyte membranes (S. Awasthiet al.,1998a,b). Our previous studies indicate a broad substrate specificity for this transport mechanism, including someP-glycoprotein substrates. Present studies were carried out to determine whether colchicine (COL), a classicalP-glycoprotein substrate, could be transported by purified human erythrocyte DNP-SG ATPase reconstituted in artificial liposomes. We also investigated whether leukotriene C4 (LTC4), an endogenous proinflammatory glutathione-conjugate derived from arachidonic acid, would inhibit colchicine transport. Uptake of COL was compared in proteoliposomes reconstituted with the purified DNP-SG ATPase as well as control liposomes in the presence or absence of ATP. Increased colchicine uptake was observed upon addition of ATP to proteoliposomes, but not control liposomes. Uptake was linear with respect to the amount of vesicle protein used. Sensitivity to osmolarity was consistent with intravesicular COL accumulation. The ATP-dependent colchicine uptake was sensitive to temperature in a manner consistent with a protein-mediated transport process with activation energy of 7.3 kcal/mol. Time-dependent COL uptake by proteoliposomes in the presence of ATP was consistent with a single compartment model with an apparent rate constant of 0.21 ± 0.02 min−1. Kinetic studies indicated a saturable behavior with respect to ATP (Km2.3 ± 0.7 mM) and colchicine (Km4.3 ± 0.2 μM). LTC4 was found to be a competitive inhibitor of COL transport (Kis16.4 μM). Since DNP-SG ATPase is present in many tissues, it may play an important role in determining colchicine accumulation in cells. Increased LTC4 would tend to increase cellular COL accumulation.

Presence of the betaII isotype of tubulin in the nuclei of cultured mesangial cells from rat kidney.

Tubulin has generally been considered to be a cytosolic protein whose only function is to form microtubules. This assumption is supported by a great deal of evidence derived from immunohistochemical studies using antibodies directed against whole tubulin or its component polypeptides alpha- and beta-tubulin. We have re-examined the intracellular distribution of tubulin using monoclonal antibodies specific for the betaI, betaII, betaIII, and betaIV isotypes of beta-tubulin. Our test system is the cultured rat kidney mesangial cell. We have found that betaIII is absent from these cells and that beta1 and betaIV are present in microtubules throughout the cytosol. In contrast, betaII is present largely in the nuclei. Immunoblotting of purified nuclear extracts shows that the betaII-reactive antigen co-migrates with beta-tubulin. Extraction of the cytosol and chromatin suggests that betaII is concentrated in the nucleoli and also in a reticulated network in the rest of the nucleoplasm. An antibody to tyrosinated alpha-tubulin shows that alpha is also present in the nucleoli. Treatment of the cells with fluorescent colchicine shows an accumulation of colchicine in the nucleoli. Finally, fluorescently labeled alphabetaII-tubulin dimers, when microinjected into the cells, enter the nuclei and are concentrated in the nucleoli. These results suggest that the betaII isotype of tubulin is present as an alphabetaII dimer in the nuclei of cultured mesangial cells and suggest the possibility that different tubulin isotypes may have specific functions within the cell.

Does the lack of the P-glycoprotein efflux pump in neutrophils explain the efficacy of colchicine in familial Mediterranean fever and other inflammatory diseases?

Colchicine is an alkaloid drug commonly used in familial Mediterranean fever (FMF), gout, Behcet's syndrome, psoriasis and Sweet's syndrome. The exact mechanism of its action in these diseases is not entirely known. However, it has been shown that colchicine may inhibit neutrophil chemotaxis, thereby decreasing the inflammatory process. Recently, it was shown that colchicine accumulates in neutrophils in higher concentrations than in lymphomonocytes. Studies dealing with the multiple drug resistance (MDR) issue disclosed that neutrophils lack the P-glycoprotein (P-gly) membranal pump (encoded by the MDR1 gene). We propose that the preferential accumulation of colchicine in neutrophils compared with lymphomonocytes is due to the absence of the P-gly efflux pump in the former. This may explain the effectiveness of colchicine in diseases where increased chemotaxis is evident. The hypothesis may also provide an explanation for FMF patients who do not respond to the drug.

Synthetic hydrophobic peptides are substrates for P-glycoprotein and stimulate drug transport.

P-Glycoprotein functions as an ATP-driven active efflux pump for many natural products and chemotherapeutic drugs. Hydrophobic peptides have been shown to block drug uptake by P-glycoprotein, indicating that they might be transport substrates. The present study examines the interaction of the synthetic peptide series NAc-LnY-amide with the multidrug transporter. Several peptides in this series caused up to 3.5-fold enhancement of colchicine accumulation in membrane vesicles from multidrug resistant (MDR) cells, which suggests the existence of novel interactions between the binding sites for peptides and drug. Peptides did not stimulate vinblastine transport, which was inhibited as expected for competing substrates. These peptides displayed modest stimulatory effects on the ATPase activity of P-glycoprotein. None blocked azidopine photoaffinity labelling, showing that they probably occupy a binding site separate from that for the drug. Studies with 125I-labelled NAc-LLY-amide showed that it was transported by P-glycoprotein in both membrane vesicles and reconstituted proteoliposomes. Uptake of the peptide was rapid, saturable, osmotically sensitive and occurred against a concentration gradient. The enhancing effect of NAc-LLY-amide on colchicine transport was reciprocated, i.e. colchicine greatly increased the transport of labelled peptide by P-glycoprotein. Peptide transport was also modulated, both positively and negatively, by other MDR spectrum drugs. It is concluded that linear hydrophobic peptides are indeed transported by P-glycoprotein, and some have interactions with drug substrates that result in mutual stimulation of transport.

Functional expression of P-glycoproteins in secretory vesicles.

We expressed P-glycoproteins (P-gps) encoded by the three mouse mdr genes in the membranes of secretory vesicles (SV) accumulating in the yeast mutant strain sec 6-4. Expression of the Mdr1 and Mdr3 isoforms in SV membranes caused a significant increased accumulation of the drug vinblastine (VBL) over background levels measured in control SV. The Mdr1/Mdr3-mediated increased drug accumulation could be completely abolished by the P-gp modulator verapamil. By contrast, overexpression of Mdr2 in these vesicles failed to increase intravesicular VBL accumulation over background levels. Mdr3-mediated VBL transport was not affected by changes in the membrane potential, since identical rates of VBL uptake were measured in the presence or absence of the endogenous proton-translocating PMA1 H(+)-ATPase responsible for the strong electrochemical membrane potential across SV membranes. Moreover, in the presence of a delta micro-H+ across the SV membranes (inside positive) of almost 90 mV, we detected in Mdr3-expressing SV an enhanced accumulation of the lipophilic cation and P-gp substrate tetraphenylphosphonium, suggesting that P-gp-mediated uptake of this cation occurs against an intravesicular depolarized membrane. Likewise, VBL transport in Mdr3-expressing SV was not affected by the presence or absence of a steep proton gradient (inside acid) and was independent of any proton movements, excluding a proton synport or antiport mechanism for P-gp-mediated drug transport. Finally, we could demonstrate that colchicine accumulation in Mdr3-expressing SV occurred against a significant substrate concentration gradient, reaching a 7-fold increase in intravesicular colchicine concentration above the extravesicular medium drug concentration. Our studies show that SV isolated from the temperature-sensitive yeast sec 6-4 mutants are an ideal tool to express and to functionally characterize heterologous membrane proteins, in general and P-gps, in particular.

Plasma kinetics and biliary excretion of colchicine in patients with chronic liver disease after oral administration of a single dose and after long-term treatment.

Plasma kinetics and biliary excretion of colchicine in patients with chronic liver disease were evaluated after oral administration of a single dose and after long-term treatment. A single oral dose of 1 mg colchicine led to a mean peak concentration of 3.60 +/- 1.04 ng/ml at a peak time of 2.16 +/- 0.34 h and a mean area under the plasma concentration time curve, extrapolated from time 0 to infinity, of 24.90 +/- 8.47 ng.h/ml. Comparable values were obtained after repeated administration. Distribution half-life was 2.83 +/- 0.74 h, and terminal plasma half-life was 9.81 +/- 2.08 h; the mean apparent volume of distribution and the mean apparent plasma clearance were 1448 +/- 4061 and 175.3 +/- 47.6 1/h, respectively. Colchicine concentrations in bile (2025 +/- 1368 ng/ml) were clearly higher than in plasma. Long-term treatment with colchicine (1 mg/day) in patients with various stages of primary biliary cirrhosis (PBC) was associated with colchicine concentrations varying from < 0.15 to 2.0 ng/ml, with a slight tendency to higher concentrations in PBC stages III-IV than I-II. Although about 20% of colchicine is excreted in bile within 24 h, accumulation of colchicine may appear only in patients with advanced liver disease and cholestasis.