Lapachol inhibition of vitamin K epoxide reductase and vitamin K quinone reductase

Complementary medicine use among general internal medicine inpatients in a Swiss university hospital

BACKGROUND

Complementary Medicine (CM) is frequently used by the general population, but data about prevalence among hospitalised patients are scarce. We evaluated the prevalence and determinants of CM use by inpatients, lifetime, 2 months before and during their hospitalisation in a general internal medicine ward.

METHODS

Cross-sectional survey conducted in September 2014 among adult (≥18 years) patients hospitalised for at least 1 day in the general internal medicine ward of the Lausanne University Hospital, Switzerland. The association between the socio-demographic data and CM used were assessed using logistic regression model.

RESULTS

Among the 289 eligible patients, 130 (45%, mean age 68.9±16.4 years, 59.2% male) were included. The lifetime prevalence of CM use was 74.6%. One-third (31.5%) and one-tenth of patients reported CM use 2 months prior or during hospitalisation, respectively. The four most reported CM used during lifetime were homeopathy (54.6%), herbal medicine (49.5%), therapeutic massage (47.4%), and osteopathy (44.3%). Herbal medicine, homeopathy, meditation and therapeutic massage were the four main CM used during hospitalisation. On bivariate analysis, lifetime use of CM was significantly associated with higher level of education (apprenticeship: OR 3.2, 95% CI [1.20-8.51], high school/university: OR 7.67, 95% CI [2.59-22.70]; P=.004) and healthcare coverage for CM (OR 3.53, 95% CI [1.32-9.46]; P=.014), but not with age and gender. During hospitalisation only 3.8% of patients were asked about CM use by physicians.

CONCLUSION

One-third of hospitalised patients used CM 2 months before hospitalisation and one-tenth during hospital stay. CM use is seldom queried by hospital staff; better assessment of CM use among hospitalised patients could prevent potential adverse events or interactions.

Cytotoxic Activity of Lomatiol and 7-(3′-Hydroxymethyl-3′-methylallyloxy)coumarin

7-(3′-Hydroxymethyl-3′-methylallyloxy)coumarin, bearing a 3′-hydroxy-3′-methylallyl group as the O-side chain, and lomatiol, a lapachol derivative sharing the same structural feature, were tested for their in vitro growth inhibitory activities on six cancer cell lines using the MTT colorimetric assay, along with the respective 3′,3′-dimethylallyl derivatives and unprenylated products used for comparison. Data revealed that lomatiol displayed the strongest growth inhibitory activities in vitro although not as efficient as the parent compound lapachol. The oxidized O-prenylcoumarin recorded better growth inhibitory capacities than the prenylated and unprenylated parent products.

Updates on the clinical evidenced herb-warfarin interactions

Increasing and inadvertent use of herbs makes herb-drug interactions a focus of research. Concomitant use of warfarin, a highly efficacious oral anticoagulant, and herbs causes major safety concerns due to the narrow therapeutic window of warfarin. This paper presents an update overview of clinical findings regarding herb-warfarin interaction, highlighting clinical outcomes, severity of documented interactions, and quality of clinical evidence. Among thirty-eight herbs, Cannabis, Chamomile, Cranberry, Garlic, Ginkgo, Grapefruit, Lycium, Red clover, and St. John's wort were evaluated to have major severity interaction with warfarin. Herbs were also classified on account of the likelihood of their supporting evidences for interaction. Four herbs were considered as highly probable to interact with warfarin (level I), three were estimated as probable (level II), and ten and twenty-one were possible (level III) and doubtful (level IV), respectively. The general mechanism of herb-warfarin interaction almost remains unknown, yet several pharmacokinetic and pharmacodynamic factors were estimated to influence the effectiveness of warfarin. Based on limited literature and information reported, we identified corresponding mechanisms of interactions for a small amount of “interacting herbs.” In summary, herb-warfarin interaction, especially the clinical effects of herbs on warfarin therapy should be further investigated through multicenter studies with larger sample sizes.

Thirteen novel VKORC1 mutations associated with oral anticoagulant resistance: insights into improved patient diagnosis and treatment

BACKGROUND

Vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) is the molecular target of oral anticoagulants. Mutations in VKORC1 cause partial or total coumarin resistance.

OBJECTIVES

To identify new VKORC1 oral anticoagulant (OAC) resistance (OACR) mutations and compare the severity of patient phenotypes across different mutations and prescribed OAC drugs.

PATIENTS/METHODS

Six hundred and twenty-six individuals exhibiting partial or complete coumarin resistance were analyzed by VKORC1 gene sequencing and CYP2C9 haplotyping.

RESULTS

We identified 13 patients, each with a different, novel human VKORC1 heterozygous mutation associated with an OACR phenotype. These mutations result in amino acid substitutions: Ala26→Thr, His28→Gln, Asp36→Gly, Ser52→Trp, Ser56→Phe, Trp59→Leu, Trp59→Cys, Val66→Gly, Gly71→Ala, Asn77→Ser, Asn77→Tyr, Ile123→Asn, and Tyr139→His. Ten additional patients each had one of three previously reported VKORC1 mutations (Val29→Leu, Asp36→Tyr, and Val66→Met). Genotyping of frequent VKORC1 and CYP2C9 polymorphisms in these patients revealed a predominant association with combined non-VKORC1*2 and wild-type CYP2C9 haplotypes. Additionally, data for OAC dosage and the associated measured International Normalized Ratio (INR) demonstrate that OAC therapy is often discontinued by physicians, although stable therapeutic INR levels may be reached at higher OAC dosages. Bioinformatic analysis of VKORC1 homologous protein sequences indicated that most mutations cluster into protein sequence segments predicted to be localized in the lumenal loop or at the endoplasmic reticulum membrane-lumen interface.

CONCLUSIONS

OACR mutations of VKORC1 predispose afflicted patients to high OAC dosage requirements, for which stable, therapeutic INRs can sometimes be attained.

The hydroxy-naphthoquinone lapachol arrests mycobacterial growth and immunomodulates host macrophages

The present study reports the anti-mycobacterial activity of 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone (lapachol) as well as its influence on macrophage functions. Lapachol (L) did not induce apoptosis/necrosis of THP-1 macrophages at ≤32 μg/mL. Mycobacterium avium liquid growth was arrested by ≥32 μg/mL and intra-macrophage proliferation by ≥16 μg/mL lapachol. The main immuno-modulatory effects of lapachol observed were an up-regulation of interferon-γ-receptor 1 (IFN-γR1) and major histocompatibility complex class II (MHCII) surface expression, and a marked inhibition of IL-10 secretion. Lapachol did not affect resting, IFN-γ- or toll-like receptor 2 (TLR2)-induced levels of oxygen and nitrogen metabolism key proteins nor the TLR2-mediated secretion of TNF-α, nor induced either oxidative or endoplasmic reticulum (ER) stress. Lapachol inhibited the surface expression of the co-stimulatory molecule CD86 but not that of CD80 and CD83. The results obtained indicate that the substituted naphthoquinone lapachol exhibits an anti-mycobacterial activity that is more efficient intra- than extra-cellularly, and exerts immuno-modulatory effects some of which may enhance the capacity of the host cell to control mycobacterial growth. The immune-modulatory action of lapachol could contribute to its more efficient intra-macrophage anti-mycobacterial activity.

Bioactivation of lapachol responsible for DNA scission by NADPH-cytochrome P450 reductase

The reduction of the naphthoquinone derivative, lapachol, which is responsible for its bioactivation was examined using microsomal preparations and NADPH-cytochrome P450 reductase (P450 reductase). Phenobarbital (PB) pretreatment resulted in an induction of enzyme activities for cytochrome c reduction (1.54 times) and lapachol reduction (1.20 times) by hepatic microsomal preparation of rats. The specific activity of lapachol reduction by purified P450 reductase showed 56-fold higher than that by untreated liver microsomes. Addition of antibody against P450 reductase (2 mg of IgG/mg of protein) to the microsomal incubation mixture caused an immunoinhibition of cytochrome c (32%) and lapachol (19%) reduction activities, suggesting that P450 reductase catalyzes lapachol reduction. Generation of superoxide anion radical (1321 nmol/mg per min) in approximately equivalent amounts of with NADPH consumption (941 nmol/mg per min) was detected during metabolism of lapachol by P450 reductase. Electron spin resonance (ESR) experiments confirmed generation of superoxide anion radical and hydroxyl radical as these 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) adducts. Incubation of lapachol with P450 reductase caused a cleavage of DNA which was reduced in the presence of Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase(1), and hydroxyl radical scavengers such as dimethyl sulfoxide (DMSO) and thiourea. Taken together, these results indicate that lapachol is bioactivated by P450 reductase to reactive species, which promote DNA scission through the redox cycling based generation of superoxide anion radical.

Radiosensitization by nickel lapachol

The properties of interest in the radiosensitization of a metal complex, nickel lapachol, are compared with those of the 2-nitroimidazole, misonidazole. These very different compounds were found to be surprisingly similar in terms of their reduction potential (-370 mV), enhancement ratios for killing of hypoxic Chinese hamster ovary cells by X-irradiation, and enhancement of DNA breaks in hypoxia. For nitroimidazoles, the sensitization depends on 'electron affinity', reduction of the nitro group; for nickel lapachol it is the metal which is necessary for reduction, yet the sensitization efficiencies are remarkably close. However, the metal complex has additional activities (some sensitization in aerobic cells; increased sensitization with preincubation) which are as yet unexplained but are assumed to be related to the nature of the naphthoquinone ligand, rather than to the reduction of the metal.

Vitamin K metabolism and nutriture

Vitamin K functions as a co-factor for the post-translational carboxylation of specific glutamate residues to gamma-carboxyglutamate (Gla) residues in several blood coagulation factors (II, VII, IX and X) and coagulation inhibitors (proteins C and S) in the liver; as well as a variety of extrahepatic proteins such as the bone protein osteocalcin. This review outlines some recent advances in our understanding of the metabolism of vitamin K and its role in human nutriture. The introduction of new methodologies to measure the low endogenous tissue concentrations of K vitamins and circulating plasma levels of des-gamma-carboxyprothrombin (PIVKA-II) have provided correspondingly more refined indices for the assessment of human vitamin K status. The assays for vitamin K have also been used to study the sources, intestinal absorption, plasma transport, storage and transplacental transfer of K vitamins and the importance of phylloquinone (vitamin K1) versus menaquinones (vitamins K2) to human needs. The ability to biochemically monitor subclinical vitamin K deficiency has reaffirmed the precarious vitamin K status of the newborn and led to an increased appreciation of the risk factors leading to haemorrhagic disease of the newborn and how this may be prevented. Biochemical studies are leading to an increased knowledge of the mode of action of traditional coumarin anticoagulants and how some unrelated compounds (e.g. antibiotics) may also antagonize vitamin K and cause bleeding. There is also an awareness of the possible deleterious effects of vitamin K antagonism or deficiency on non-hepatic Gla-proteins which may play some subtle role in calcium homeostasis.

Vitamin K epoxide and quinone reductase activities. Evidence for reduction by a common enzyme

Vitamin K hydroquinone formation in rat liver can be catalyzed by a thiol-dependent quinone reductase activity which shares several characteristics with the vitamin K 2,3-epoxide reductase activity. The possibility that a single enzyme catalyzes both reductions was investigated. Values of Vmax/Km for several different vitamin K analogs were determined and found to be similar for both reductase activities. Several different coumarins were also shown to achieve 50% inhibition at similar concentrations for both enzyme activities. The chloro analog of menaquinone-2 was shown to inhibit both reductases, and the presence of either the quinone or epoxide form of the vitamin protected both activities from inactivation. Thioredoxin was shown to function as a reductant for both reductase activities, although the maximum enzyme activity achieved by this reductant was only half that achieved with dithiothreitol as a reductant. Cofractionation of the two reductase activities on a variety of column matrices was also observed. These data strongly support the hypothesis that one microsomal enzyme is capable of catalyzing both reduction of vitamin K 2,3-epoxide to the quinone, and the quinone to vitamin K hydroquinone.

Vitamin K1 2,3-epoxide and quinone reduction: mechanism and inhibition

The chemical and enzymatic pathways of vitamin K1 epoxide and quinone reduction have been investigated. The reduction of the epoxide by thiols is known to involve a thiol-adduct and a hydroxy vitamin K enolate intermediate which eliminates water to yield the quinone. Sodium borohydride treatment resulted in carbonyl reduction generating relatively stable compounds that did not proceed to quinone in the presence of base. NAD(P)H:quinone oxidoreductase (DT-diaphorase, E.C. 1.6.99.2) reduction of vitamin K to the hydroquinone was a significant process in intact microsomes, but 1/5th the rate of the dithiothreitol (DTT)-dependent reduction. No evidence was found for DT-diaphorase catalyzed reduction of vitamin K1 epoxide, nor was it capable of mediating transfer of electrons from NADH to the microsomal epoxide reducing enzyme. Purified diaphorase reduced detergent- solubilized vitamin K1 10(-5) as rapidly as it reduced dichlorophenylindophenol (DCPIP). Reduction of 10 microM vitamin K1 by 200 microM NADH was not inhibited by 10 microM dicoumarol, whereas DCPIP reduction was fully inhibited. In contrast to vitamin K3 (menadione), vitamin K1 (phylloquinone) did not stimulate microsomal NADPH consumption in the presence or absence of dicoumarol. DTT-dependent vitamin K epoxide reduction and vitamin K reduction were shown to be mutually inhibitory reactions, suggesting that both occur at the same enzymatic site. On this basis, a mechanism for reduction of the quinone by thiols is proposed. Both the DTT-dependent reduction of vitamin K1 epoxide and quinone, and the reduction of DCPIP by purified DT-diaphorase were inhibited by dicoumarol, warfarin, lapachol, and sulphaquinoxaline.

Sulfaquinoxaline inhibition of vitamin K epoxide and quinone reductase

Sulfaquinoxaline (N1-(2-quinoxalinyl)sulfanilamide) has been shown to be a potent (Ki = 1 microM) freely reversible inhibitor of the dithiothreitol-dependent reduction of both vitamin K epoxide and vitamin K quinone by rat liver microsomes in vitro. This observation provides an explanation for the hemorrhagic syndrome occasionally seen in poultry on medicated feed and the efficacy of sulfaquinoxaline in anticoagulant based rodenticides. Sulfaquinoxaline inhibition resembled inhibition by coumarin anticoagulants (e.g., warfarin) and hydroxynaphthoquinones (e.g., lapachol). Inhibition was observed in assays using microsomes from control strain rats, but the enzyme was resistant to sulfaquinoxaline in microsomes from warfarin-resistant rats. Steady-state kinetics inhibition patterns were nearly competitive versus dithiothreitol and nearly uncompetitive versus vitamin K epoxide as is observed for warfarin and lapachol. These results suggest that this inhibitor binds to the oxidized form of vitamin K epoxide reductase in the same way as suggested for the coumarins and hydroxyquinones. Of 10 other sulfa drugs tested, none were inhibitors, and of fragments and related compounds tested, only 2-aminoquinoxaline benzenesulfonamide was active. These results provide a probably orientation in the binding site in relation to that for warfarin and lapachol.

Lapachol inhibition of DT-diaphorase (NAD(P)H:quinone dehydrogenase)

Lapachol has been found to be a potent inhibitor of the enzyme DT-Diaphorase. Inhibition is competitive versus NADH, Ki = 0.15 microM. Lapachol was not a good substrate for cytochrome P450 reductase, thus inhibition of DT-Diaphorase should not promote its metabolism via radical generating pathways. DT-Diaphorase has been used to test a lapachol affinity chromatography column designed for purification of another coumarin anticoagulant and lapachol sensitive enzyme, vitamin K epoxide reductase.