Inhibition of delayed hypersensitivity reactions in mice by colchicine. I. Mechanism of inhibition of contact sensitivity in vivo

Cell Surface Binding and Lipid Interactions behind Chemotherapy-Drug-Induced Ion Pore Formation in Membranes

Chemotherapy drugs (CDs) disrupt the lipid membrane’s insulation properties by inducing stable ion pores across bilayer membranes. The underlying molecular mechanisms behind pore formation have been revealed in this study using several methods that confirm molecular interactions and detect associated energetics of drugs on the cell surface in general and in lipid bilayers in particular. Liposome adsorption and cell surface binding of CD colchicine has been demonstrated experimentally. Buffer dissolved CDs were considerably adsorbed in the incubated phospholipid liposomes, measured using the patented ‘direct detection method’. The drug adsorption process is regulated by the membrane environment, demonstrated in cholesterol-containing liposomes. We then detailed the phenomenology and energetics of the low nanoscale dimension cell surface (membrane) drug distribution, using atomic force microscopy (AFM) imaging what addresses the surface morphology and measures adhesion force (reducible to adhesive energy). Liposome adsorption and cell surface binding data helped model the cell surface drug distribution. The underlying molecular interactions behind surface binding energetics of drugs have been addressed in silico numerical computations (NCs) utilizing the screened Coulomb interactions among charges in a drug–drug/lipid cluster. Molecular dynamics (MD) simulations of the CD-lipid complexes detected primarily important CD-lipid electrostatic and van der Waals (vdW) interaction energies. From the energetics point of view, both liposome and cell surface membrane adsorption of drugs are therefore obvious findings. Colchicine treated cell surface AFM images provide a few important phenomenological conclusions, such as drugs bind generally with the cell surface, bind independently as well as in clusters of various sizes in random cell surface locations. The related adhesion energy decreases with increasing drug cluster size before saturating for larger clusters. MD simulation detected electrostatic and vdW and NC-derived charge-based interactions explain molecularly of the cause of cell surface binding of drugs. The membrane binding/association of drugs may help create drug–lipid complexes with specific energetics and statistically lead to the creation of ion channels. We reveal here crucial molecular understanding and features of the pore formation inside lipid membranes that may be applied universally for most of the pore-forming existing agents and novel candidate drugs.

The Antimicrobial Peptide Gramicidin S Enhances Membrane Adsorption and Ion Pore Formation Potency of Chemotherapy Drugs in Lipid Bilayers

We recently published two novel findings where we found the chemotherapy drugs (CDs) thiocolchicoside (TCC) and taxol to induce toroidal type ion pores and the antimicrobial peptide gramicidin S (GS) to induce transient defects in model membranes. Both CD pores and GS defects were induced under the influence of an applied transmembrane potential (≈100 mV), which was inspected using the electrophysiology record of membrane currents (ERMCs). In this article, I address the regulation of the membrane adsorption and pore formation of CDs due to GS-induced possible alterations of lipid bilayer physical properties. In ERMCs, low micromolar (≥1 μM) GS concentrations in the aqueous phase were found to cause an induction of defects in lipid bilayers, but nanomolar (nM) concentration GS did nothing. For the binary presence of CDs and GS in the membrane-bathing aqueous phase, the TCC pore formation potency is found to increase considerably due to nM concentration GS in buffer. This novel result resembles our recently reported finding that due to the binary aqueous presence of two AMPs (gramicidin A or alamethicin and GS), the pore or defect-forming potency of either AMP increases considerably. To reveal the underlying molecular mechanisms, the influence of GS (0-400 nM) on the quantitative liposome (membrane) adsorption of CD molecules, colchicine and TCC, was tested. I used the recently patented direct detection method, which helps detect the membrane active agents directly at the membrane in the mole fraction relative to its concentrations in aqueous phase. We find that GS, at concentrations known to do nothing to the lipid bilayer electrical barrier properties in ERMCs, increases the membrane adsorption (membrane uptake) of CDs considerably. This phenomenological finding along with the GS effects on CD-induced membrane conductance increase helps predict an important conclusion. The binary presence of AMPs alongside CDs in the lipid membrane vicinity may work toward enhancing the physical adsorption and pore formation potency of CDs in lipid bilayers. This may help understand why CDs cause considerable cytotoxicity.

Isolation and anti-inflammatory activity of colchicinoids from Gloriosa superba seeds

Gloriosa superba L. (Liliaceae) seeds, known as "kalihari" (Hindi), were phytochemically investigated for colchicine (well known for gout treatment) and other related alkaloid content. Colchicine, 2- demethylcolchicine, 3-demethylcolchicine, and N-formyl-N-deacetylcolchicine were alkaloids isolated from the seeds. The isolated samples have been standardized for their purity with respect to the reference standard using HPLC. The structures were confirmed by NMR spectroscopy and were analyzed by spiking them along with colchicine reference by HPLC. The purity of colchicine, 2- demethylcolchicine, 3- demethylcolchicine and N-formyl-N-deacetylcolchicine were 99.82, 96.78, 98.71, and 98.13% respectively. The compounds were subjected to an anti-inflammatory study by using the formaldehyde inflammagen-induced inflammation model. Oral administration of colchicine at 2, 4, and 6 mg/kg body weight resulted in 48.9, 68.7, and 79.1% inhibition respectively, while 30.9% inhibition was seen in the phenylbutazone 100 mg/kg treated group once daily for a period of 4 days. The results clearly indicated that the colchicine is more effective as an anti-inflammatory agent compared with phenylbutazone, the standard drug used in the study, whereas the oral administration of 6 mg/kg body weight of 2- demethylcolchicine, 3-demethylcolchicine and N-formyl-N-deacetylcolchicine showed very poor activity (41.6, 40.4, and 41.1% activity respectively).

Discovery of novel immunostimulants by dendritic-cell-based functional screening

Immunostimulants represent an emerging class of drugs for the treatment of infectious disorders and cancer. CpG oligonucleotides and imiquimod, prototypic drugs in this category, are now known to activate dendritic cells (DCs). Here we report the development of a highly sensitive, unbiased functional screen to detect DC-stimulatory signals. Because interleukin-1beta (IL-1beta) mRNA expression is closely associated with DC activation, we engineered DCs to stably express a fluorescent marker gene under the control of IL-1beta promoter. By screening about 3000 compounds with the resulting DC biosensor clone, we identified DC-stimulatory potentials of topoisomerase I inhibitors (camptothecin derivatives) and microtubule depolymerizing drugs (colchicine and podophyllotoxin). In response to treatment with each agent, bone marrow-derived DC preparations exhibited characteristic phenotypic and/or functional changes associated with DC activation. All of these agents also triggered nuclear factor-kappaB (NFkappaB) activation in DCs, suggesting a common pharmacologic mechanism of action. Furthermore, locally administered colchicine induced in situ maturation and migration of DCs and augmented both humoral and cellular immune responses. These results support the practical utility of the DC-based biosensor system to discover novel DC-targeted immunostimulants and unveil previously unrecognized (and totally unexpected) pharmacologic activities of several drugs that are commonly used for the treatment of various disorders.

Update on colchicine and its mechanism of action

Colchicine is a unique anti-inflammatory drug with respect to its limited clinical usefulness and its mode of action. Colchicine is mainly indicated for the treatment and prophylaxis of gout and familial Mediterranean fever. Its mode of action includes modulation of chemokine and prostanoid production and inhibition of neutrophil and endothelial cell adhesion molecules by which it interferes with the initiation and amplification of the joint inflammation. This paper discusses its adverse effects and indications.

Colchicine and griseofulvin inhibit VCAM-1 expression on human vascular endothelial cells - evidence for the association of VCAM-1 expression with microtubules

We have previously reported that griseofulvin inhibits VCAM-1 expression on human vascular endothelial cells. Since griseofulvin interferes with microtubule assembly, we used colchicine as another microtubule antagonist and compared it with griseofulvin to further characterize this inhibition. By flow cytometry, colchicine inhibited VCAM-1 induction on TNFalpha-stimulated human dermal microvascular endothelial cells (HDMEC) dose-dependently. Colchicine also inhibited VCAM-1 induction on both TNFalpha- and IL-1alpha-stimulated human umbilical vein endothelial cells (HUVEC). Although this inhibition was reversible, colchicine-treated cells showed slower restoration of its expression than griseofulvin-treated cells. Moreover, co-incubation with a microtubule stabilizer paclitaxel blocked this inhibition, and colchicine-treated cells were more resistant to this blocking than griseofulvin. RT-PCR of HDMEC showed inhibition of the transcript level of VCAM-1 by both antagonists. These results indicate intimate association between VCAM-1 expression and microtubules.

Characterization of kinectin, a kinesin-binding protein: primary sequence and N-terminal topogenic signal analysis

Kinectin is a kinesin-binding protein (Toyoshima et al., 1992) that is required for kinesin-based motility (Kumar et al., 1995). A kinectin cDNA clone containing a 4.7-kilobase insert was isolated from an embryonic chick brain cDNA library by immunoscreening with a panel of monoclonal antibodies. The cDNA contained an open reading frame of 1364 amino acids encoding a protein of 156 kDa. A bacterially expressed product of the full length cDNA bound purified kinesin. Transient expression in CV-1 cells gave an endoplasmic reticulum distribution that depended upon the N-terminal domain. Analysis of the predicted amino acid sequence indicated a highly hydrophobic near N-terminal stretch of 28 amino acids and a large portion (326-1248) of predicted alpha helical coiled coils. The 30-kDa fragment containing the N-terminal hydrophobic region was produced by cell-free in vitro translation and found to assemble with canine pancreas rough microsomes. Cleavage of the N terminus was not observed confirming its role as a potential transmembrane domain. Thus, the kinectin cDNA encodes a cytoplasmic-oriented integral membrane protein that binds kinesin and is likely to be a coiled-coil dimer.

Horizons in pharmacologic intervention in allergic contact dermatitis

The treatment of allergic contact dermatitis remains a major challenge. Current management strategies consist of elimination of the allergen when possible and therapy for symptoms with topical or systemic corticosteroids. With increasing exposure of the human skin to environmental antigens and haptens, more selective treatment options are needed. Advances in the elucidation of the skin immune system and of the cellular and molecular events in immunologic processes may allow targeted methods of controlling delayed hypersensitivity reactions. This review focuses on mechanisms of established therapeutic agents and new developments, such as FK 506 (tacrolimus), pentoxifylline, and vitamin D3 derivative, for suppression of any phase of allergic contact dermatitis.

A clinical study of colchicine in childhood asthma

A double-blind, randomized, crossover study was done to determine the efficacy of colchicine in 30 atopic children with moderately severe asthma. A constant dose of sustained-release theophylline and salbutamol by inhalation, as needed, was administered to all patients. Compared to placebo, colchicine, 0.5 mg twice daily, significantly reduced morning tightness and nocturnal asthma score. There was, however, no significant difference between colchicine and placebo for cough, daytime asthma, or daily combined symptom scores for each patient. Colchicine did not significantly decrease beta-2 agonist inhaler use when compared with placebo. Similarly, there was no statistically significant difference between placebo and colchicine therapy as far as pulmonary function tests and peak flow reversibility were concerned. Thus, colchicine administered for 4 weeks demonstrated insufficient antiasthma activity. Colchicine-induced clinical improvement that was reported in a previous study may be due to selection of patients with mild asthma symptoms. However, our group, comprised of moderately severe asthmatic patients, did not show a satisfactory clinical response.