SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
The photomutagenicity of the furochromone khellin was tested in Ames Salmonella strains using 8-methoxypsoralen (8-MOP) and 4,5', 8-trimethylpsoralen (TMP) as positive controls. When khellin was assayed with strain TA1537, mutation induction was not detectable; in the same strain, an equitoxic dose (52-56% level of survival) of TMP (used at a concentration 12-fold lower than khellin and with a UVA dose 83-fold lower than that used with khellin) yielded an increase in revertants/plate 3-fold above the spontaneous background. In strain TA102, khellin plus UVA treatment yielded a 2-fold increase in revertants/plate above the spontaneous background (79% survival). 8-MOP, however, used at a concentration 8-fold lower than khellin with a UVA dose 13-fold lower than khellin, yielded an increase in revertants/plate about 14-fold above background (66% survival) in the same strain. These data show that khellin has a weak photomutagenic potential and, along with the previously reported low photogenotoxic potential in eukaryotic cell systems, support the notion that khellin may be safer than bifunctional psoralens for clinical use.
Khellin and khelloside (khellol glucoside) were examined in female cynomolgus monkeys to substantiate their ability to favorably modify serum lipoprotein cholesterol. Clinical chemistry parameters were also measured to obtain information indicative of possible drug toxicity. Both drugs were evaluated in two week multiple-dose studies and after a single oral dose. After two weeks at 20 mg/kg per day, khellin and khelloside significantly lowered low density lipoprotein cholesterol (LDL-C) by 87% and 73%, high density lipoprotein cholesterol (HDL-C) by 41% and 23%, and total-C by 55% and 44%, respectively. Very low density lipoprotein cholesterol (VLDL-C) and triglycerides (TG) were not changed. No apparent toxicity was observed as clinical chemistry parameters and body weights were not different compared to control values. Similar results were observed with lower doses of khellin and khelloside. Khellin at 5 mg/kg per day reduced LDL-C by 50%, HDL-C by 15%, and total-C by 30%, while khellol glucoside at 10 mg/kg per day lowered LDL-C by 46%, HDL-C by 20%, and total-C by 31%. Neither drug produced significant changes in VLDL-C, TG, body weights, or clinical chemistry variables. A 2 mg/kg per day dose of khellin also had no observable effect in this study. Single oral doses (20 mg/kg) of khellin and khelloside caused modulation of LDL-C (-32% and -30%) and total-C (-18% and -15%). Visual observation of the monkeys during this study revealed that khellin caused emesis in 9/9 animals, while khelloside and control had no emetic effect.(ABSTRACT TRUNCATED AT 250 WORDS)
The furocoumarin, 4,5',8-trimethylpsoralen, sensitizes cells and viruses to 360 nm light, producing cross-links and monoadducts in their DNA. The furanochromone khellin is a less effective sensitizing agent than psoralen, but has been found to induce cross-links and adducts in DNA also. The number of cross-links increases as the square of the time of exposure to light. We found that greater fluences were required for khellin than for psoralen, possibly because of the less favorable angle of the distal unsaturated bonds for corss-linking pyrimidines in adjacent base pairs. By adjusting the time of exposure to 360 nm light, lambda phages were damaged with [3H]psoralen and [3H]khellin so as to produce equal numbers of cross-links. These exposures were found to produce 8-times more [3H]khellin than [3H]psoralen adducts in the DNA of the phages. Similar exposures were made with nonradioactive photosensitizers to determine the effectiveness of lambda phages carrying cross-links and monoadducts in producing genetic recombinants. Lambda phage-prophage genetic corsses were performed with psoralen and khellin-damaged phages under repressed conditions in which replication of the damaged DNA was blocked. It was estimated from the results that cross-links were about 20-times more effective than monoadducts for inducing recombination under repressed conditions. In tests on the survival of plaque forming ability on wild type bacteria, it was estimated that cross-links were about 15-times more effective than the adducts. The results support the conclusion that, in homoimmune crosses with psoralen-damaged lambda phages infecting wild type lysogens, more than three-quarters of the induced recombination can be attributed to cross-links rather than to monoadducts.
Twenty-eight patients with vitiligo were treated with a new photochemotherapeutic regimen using khellin, a furanochromone, as photosensitizer, together with ultraviolet A (UVA) irradiation. Twenty-five patients received khellin orally and three patients were treated with topical khellin. Treatments were given three times weekly. As opposed to psoralens, khellin did not induce skin phototoxicity with UVA but it induced repigmentation similar to psoralens. The treatment success strongly depended on the number of treatments. More than 70% repigmentation was achieved in 41% of the patients who had received 100 to 200 treatments. This success rate is comparable to the rate obtained with psoralens. Seven patients experienced a mild elevation of liver transaminases within the early treatment phase and their treatments were discontinued. No long-term internal organ or skin toxicity was observed. The major advantage of khellin is that it does not lead to phototoxic skin erythema and thus can be considered safe for home treatment. Because of its photochemistry it may be considered less hazardous than psoralens regarding mutagenicity and carcinogenicity.
To clarify the mechanism of the vasodilatory action of khellin on calcium, we have investigated its relaxant action on base line and on K+ and noradrenaline-induced contractile tensions in rat aorta smooth muscle and on spontaneous contractile activity of rat portal vein. Khellin relaxed both of these preparations with a similar potency, which suggests a non-specific inhibition of calcium flux, without any difference related to the specific calcium channels. We have also studied the capacity of khellin to interfere with the loading and release mechanisms of caffeine and noradrenaline-sensitive calcium stores in Ca-free medium. Khellin's Ca2+ loading reduction may be related with its capacity to inhibit calcium influx. Khellin applied during Ca2+ release also caused relaxation. We propose that this drug may enhance calcium extrusion or sequestration rather than the calcium release mechanism. These actions on calcium influx and intracellular mobilization can contribute to its vasorelaxant action.
In order to evaluate the efficacy of topical khellin the vitiligo macules of one side only were painted in 41 patients with a 2% solution of khellin in acetone and propylene glycol (90 and 10%, respectively) and exposed to sunlight for a period of 4 months with 3 weekly applications and with exposure times up to 90 min. The macules of the other side were treated in 36 of the 41 patients with acetone and propylene glycol only and sun-exposed with the same schedule, while in the remaining 5 patients they were neither treated with khellin or placebo nor sun-exposed. No significant difference was evidenced between the khellin and placebo-treated sides: no excellent result (repigmentation more than 75% of the affected area) was found, and good results (repigmentation more than 50%) were found in 24.9% of khellin- plus sunlight-treated macules and in 22.3% of placebo- plus sunlight-treated macules.
High performance liquid chromatographic methods for the individual determination of khellin, phenobarbitone and dipyrone in tablets are presented. The methods specify a reverse phase column: methanol + water (68 + 32) as mobile phase at a flow rate of 0.7 ml/min with detection at 254 nm for khellin, visgnagin and dipyrone; water + ammonia + methanol (94.5 + 0.5 + 5) as a mobile phase at a flow rate of 0.7 ml/min with detection at 240 nm for phenobarbitone. At sensitivity of 0.01 AUFS, linearity ranges were found to be 0.5-4 micrograms/ml for khellin, 2.5-12.5 micrograms/ml for dipyrone and 1-7 micrograms/ml for phenobarbitone and with relative standard deviations less than 2%. The mean percentage recoveries +/- SD of khellin, dipyrone and phenobarbitone added to tablets were found to be 101.0 +/- 0.65, 100.0 +/- 0.74 and 99.9 +/- 0.74, respectively. The system can detect 2% w/w visnagin in khellin.
An improved, simple, selective, and sensitive reversed-phase high-performance liquid chromatographic (HPLC) assay for khellin and visnagin in Ammi visnaga L. fruits was developed by using an internal standardized technique. The HPLC column was a reversed-phase microBondapack C18 column, the mobile phase was water: methanol:acetonitrile (49:49:2), and the flow rate was 1.5 mL/min. Khellin and visnagin were detected and analyzed with a spectrophotometer set at 250 nm. Results of the HPLC analysis indicate a relative standard deviation of less than 0.04%. The analytical procedure was used for the quantification of khellin in various pharmaceutical dosage forms, such as ampules, tablets, and suppositories, with relative standard deviations of 1.2, 1.4, and 1.7%, respectively. As little as 10 ng of khellin or visnagin could be detected accurately in less than 13 min.
The effects of khellin on contractile responses and 45Ca2+ flux have been studied in rat isolated aortae. Khellin (10(-5)-3.2 x 10(-4) M) produced a concentration-dependent inhibition of noradrenaline (10(-6) M) and high K+ (80 mM)-induced contractions. At 3.2 x 10(-4) M, khellin increased cAMP levels and reduced 45Ca2+ influx in resting tissues and in tissues stimulated by noradrenaline (10(-5) M) and high K+ without affecting basal 45Ca2+ efflux or noradrenaline induced 45Ca2+ efflux. It is concluded that in rat isolated aorta, khellin caused a non-specific inhibition of Ca2+ influx but may also exhibit intracellular actions, thus decreasing the availability of Ca2+ required for activation. One or more of these mechanisms may be related to an increase in intracellular cAMP levels.
Khellin (CAS 82-02-0) and methoxsalen (CAS 298-81-7) were examined in male albino rats to evaluate their ability to modify serum lipoprotein cholesterol. Clinical chemistry parameters were also measured to obtain information indicative of possible drug toxicity. The drugs were evaluated in four-week double dose studies. After four weeks at 0.45 mg/100 mg b.wt. for khellin and 0.27 mg/100 g b.wt. for methoxsalen, per day, both drugs significantly lowered low density lipoprotein cholesterol, high density lipoprotein cholesterol and total cholesterol. Very low density lipoprotein cholesterol and triglycerides were not changed. No apparent toxicity was observed as clinical chemistry parameters and body weights were not different compared to control values. Similar results were observed with a lower dose of khellin (0.23 mg/100 g b.wt./d). A dose of 0.13 mg/100 g b.wt./d of methoxsalen had no observable effect in this study. Confirmation of the hypocholesterolemic activity of khellin and methoxsalen in this study enhances the therapeutic potential of these compounds against atherosclerosis.
Khellin, a naturally occurring furochromone, used in the past as a coronary vasodilator, has recently been used in the photochemotherapeutic treatment of vitiligo and psoriasis. With the aim of elucidating its mechanism of action, the interactions both in ground and excited states between the drug and DNA were studied in vitro. Khellin forms in the dark a molecular complex with DNA. By subsequent irradiation (365 nm) the drug photoconjugates covalently with the macromolecule, although the rate of photobinding is rather low. The in vivo photobinding of khellin to the DNA of Ehrlich ascites tumor cells is also low. In photoaddition with the macromolecule the drug forms inter-strand cross-links, although again in small amounts. The furan side monoadduct between khellin and thymine, formed in the photoreaction between the drug and DNA, was isolated and characterized, and shows a cis-syn configuration.
The two furanochromones khellin and visnagin react with DNA under irradiation by 365 nm light, forming photoadducts. Recently, the use of khellin as therapeutic agent for skin diseases has been proposed. It is well known that during the formation of photoadducts toxic active oxygen forms are produced. We studied therefore the behaviour of the two furanochromones as producers of 1O-2 and O-2. Our results indicate that visnagin is a strong generator of both superoxide radicals and singlet oxygen, while khellin does not exhibit strong production of OO-2, which is promptly quenched by superoxide dismutase.
The furanochromones khellin and visnagin have been characterised by 1H and 13C mono- and bidimensional NMR spectroscopies. Their strong affinity with DNA was experimentally confirmed by the complete disappearance of the furano-chromones' NMR signals upon additions of DNA. An intermolecular interaction between furanochromones and the thymidyl moieties of DNA, stabilized by the formation of a hydrogen bond between the thymidyl NH hydrogen and the C = O group of khellin or visnagin, is here proposed. This is suggested by the strong donor-acceptor behavior of these two molecular moieties, as pointed out by a selective 1H-13C Overhauser effect study of the khellin-thymidine model system.
The sequence specificity in the in vitro DNA photobinding of khellin and visnagin, two naturally occurring furochromones proposed for chemotherapy of vitiligo, was investigated by using DNA sequencing methodology. The 3'-5' exonuclease associated with the T4 DNA polymerase served as a tool for determining photoadducts distribution on DNA fragments of the lac I gene of Escherichia coli. The photoadduct distribution of psoralen is also studied for comparison. Upon UVA irradiation, visnagin mainly forms monoadducts with thymine and to a lower extent with cytosine. Alternating (A-T)n sequences are hot spots for visnagin photoaddition. This is a property shared with furocoumarins. TTT sites are also quite reactive to visnagin, as they are to methylated angelicins. In contrast, with psoralen derivatives, there is no preferential photobinding in 5'-TpA sites, and 5'-ApT sites react as well. Furthermore, many sites such as T in the GC context, and C in any context, react, although weakly. The visnagin photoadduct distribution resembles very much the photoadduct distribution of methylated angelicins as described by Miolo et al. The photoreaction of these two series of compounds is less sequence dependent than the photobinding of psoralen derivatives as described by Sage and Moustacchi and by Boyer et al. The sequence specificity in khellin-DNA photobinding is the same as for visnagin, even though it forms much fewer photoadducts. The absence of photo-oxidation of DNA after treatment with visnagin or khellin plus UVA suggests that furochromones do not present any photodynamic effect on DNA.
Khellin, whose chemical structure closely resembles that of psoralen, is reported to be an efficient drug for treating vitiligo when combined with ultraviolet A irradiation. Photobiological activity on yeast is found to be much lower than that of bifunctional psoralens such as 5-methoxypsoralen. In vitro experiments reveal that khellin is a poor photosensitizer. It behaves as a monofunctional agent with respect to DNA photoaddition. It does not photoinduce cross-links in DNA in vitro or in Chinese hamster cells in vivo. This behavior may explain the low photogenotoxicity in yeast and the lack of phototoxic erythemal response when treating vitiligo with khellin.
Timefurone and khellin (10 mg/kg/day, gavage, 14 days) significantly lowered low density lipoprotein cholesterol, high density lipoprotein cholesterol, and total cholesterol. Khellin-induced changes were significantly greater than those induced by timefurone. Neither drug altered body weights or clinical chemistry parameters. Monkeys treated with khellin, however, exhibited elevated levels of very low density lipoprotein cholesterol and marked emesis, while no changes were observed with timefurone. On the basis of these data, timefurone has a better therapeutic ratio and further study with this promising drug appears warranted.
Spectrophotometric assays are proposed for the determination of 3-dimethylaminomethylkhellin hydrochloride and khellin in bulk chemical and dosage forms. The acid dye method, using methyl orange at pH5, is applied to assay the amine in the form of an ion-pair extractable in chloroform with maximum abosrbance at 420 nm. The perchloric acid method, depending on formation and extraction of the oxonium salts of both compounds, is used to assay the amine and khellin at 333 or 430 nm and at 325 or 410 nm, respectively. The reineckate method can be used to assay the amine as the reineckate derivative in acetone with maximum absorbance at 530 nm. However, small amounts of the amine (1.5--3 mg) can be determined as the reineckate in methanol with maximum absorbance at 245 nm. Stability determination of the two compounds can be done by the acid dye and perchloric acid methods. The three methods are sufficiently accurate, sensitive, and precise.