Reduction of dapsone hydroxylamine to dapsone during methaemoglobin formation in human erythrocytes in vitro--II. Movement of dapsone across a semipermeable membrane into erythrocytes and plasma

Seabra PS, Fonseca ADN, de Azevedo Sousa KM, de Oliveira SBB, Carneiro ADS, Coleman MD, Monteiro MC. Alpha-Lipoic Acid and Its Enantiomers Prevent Methemoglobin Formation and DNA Damage Induced by Dapsone Hydroxylamine: Molecular Mechanism and Antioxidant Action

Dapsone (DDS) therapy can frequently lead to hematological side effects, such as methemoglobinemia and DNA damage. In this study, we aim to evaluate the protective effect of racemic alpha lipoic acid (ALA) and its enantiomers on methemoglobin induction. The pre- and post-treatment of erythrocytes with ALA, ALA isomers, or MB (methylene blue), and treatment with DDS-NOH (apsone hydroxylamine) was performed to assess the protective and inhibiting effect on methemoglobin (MetHb) formation. Methemoglobin percentage and DNA damage caused by dapsone and its metabolites were also determined by the comet assay. We also evaluated oxidative parameters such as SOD, GSH, TEAC (Trolox equivalent antioxidant capacity) and MDA (malondialdehyde). In pretreatment, ALA showed the best protector effect in 2.5 µg/mL of DDS-NOH. ALA (1000 µM) was able to inhibit the induced MetHb formation even at the highest concentrations of DDS-NOH. All ALA tested concentrations (100 and 1000 µM) were able to inhibit ROS and CAT activity, and induced increases in GSH production. ALA also showed an effect on DNA damage induced by DDS-NOH (2.5 µg/mL). Both isomers were able to inhibit MetHb formation and the S-ALA was able to elevate GSH levels by stimulating the production of this antioxidant. In post-treatment with the R-ALA, this enantiomer inhibited MetHb formation and increased GSH levels. The pretreatment with R-ALA or S-ALA prevented the increase in SOD and decrease in TEAC, while R-ALA decreased the levels of MDA; and this pretreatment with R-ALA or S-ALA showed the effect of ALA enantiomers on DNA damage. These data show that ALA can be used in future therapies in patients who use dapsone chronically, including leprosy patients.

Dapsone in dermatology and beyond

Dapsone (4,4′-diaminodiphenylsulfone) is an aniline derivative belonging to the group of synthetic sulfones. In 1937 against the background of sulfonamide era the microbial activity of dapsone has been discovered. Shortly thereafter, the use of dapsone to treat non-pathogen-caused diseases revealed alternate antiinflammatory mechanisms that initially were elucidated by inflammatory animal models. Thus, dapsone clearly has dual functions of both: antimicrobial/antiprotozoal effects and anti-inflammatory features similarly to non-steroidal anti-inflammatory drugs. The latter capabilities primarily were used in treating chronic inflammatory disorders. Dapsone has been investigated predominantly by in vitro methods aiming to get more insights into the effect of dapsone to inflammatory effector cells, cytokines, and/or mediators, such as cellular toxic oxygen metabolism, myoloperoxidase-/halogenid system, adhesion molecules, chemotaxis, membrane-associated phospholipids, prostaglandins, leukotrienes, interleukin-8, tumor necrosis factor α, lymphocyte functions, and tumor growth. Moreover, attention has been paid to mechanisms by which dapsone mediates effects in more complex settings like impact of lifespan, stroke, glioblastoma, or as anticonvulsive agent. Additionally, there are some dermatological investigations in human being using dapsone and its metabolites (e.g., leukotriene B₄-induced chemotaxis, ultraviolet-induced erythema). It could be established that dapsone metabolites by their own have anti-inflammatory properties. Pharmacology and mechanisms of action are determining factors for clinical use of dapsone chiefly in neutrophilic and/or eosinophilic dermatoses and in chronic disorders outside the field of dermatology. The steroid-sparing effect of dapsone is useful for numerous clinical entities. Future avenues of investigations will provide more information on this fascinating and essential agent.

1,4-naphthoquinones and other NADPH-dependent glutathione reductase-catalyzed redox cyclers as antimalarial agents

The homodimeric flavoenzyme glutathione reductase catalyzes NADPH-dependent glutathione disulfide reduction. This reaction is important for keeping the redox homeostasis in human cells and in the human pathogen Plasmodium falciparum. Different types of NADPH-dependent disulfide reductase inhibitors were designed in various chemical series to evaluate the impact of each inhibition mode on the propagation of the parasites. Against malaria parasites in cultures the most potent and specific effects were observed for redox-active agents acting as subversive substrates for both glutathione reductases of the Plasmodium-infected red blood cells. In their oxidized form, these redox-active compounds are reduced by NADPH-dependent flavoenzyme-catalyzed reactions in the cytosol of infected erythrocytes. In their reduced forms, these compounds can reduce molecular oxygen to reactive oxygen species, or reduce oxidants like methemoglobin, the major nutrient of the parasite, to indigestible hemoglobin. Furthermore, studies on a fluorinated suicide-substrate of the human glutathione reductase indicate that the glutathione reductase-catalyzed bioactivation of 3-benzylnaphthoquinones to the corresponding reduced 3-benzoyl metabolites is essential for the observed antimalarial activity. In conclusion, the antimalarial lead naphthoquinones are suggested to perturb the major redox equilibria of the targeted cells. These effects result in developmental arrest of the parasite and contribute to the removal of the parasitized erythrocytes by macrophages.

The blood-brain barrier: In vitro methods and toxicological applications

The blood-brain barrier (BBB) is reviewed with reference to in vitro cell culture models and their use and potential use in toxicological studies. The structure, function and in vitro study of brain microvessel endothelial cells (BMEC) is briefly described, as well as the effects of a number of xenobiotics, such as solvents, metals, polycations and herbicides, on the viability and barrier function of the BBB model. The biotransformation of xenobiotics is increasingly thought to be responsible for many toxic reactions seen in living systems. Few studies have addressed the effects of the products of biotransformation on the integrity of the barrier model. Many of the specific human bioactivating enzymes, such as cytochrome P-450s, can now be conveniently studied in eukaryotic in vitro gene expression systems. The combination of such systems with a well characterized porcine BMEC culture model might be useful in the study of reactive metabolites on the BBB, in terms of changes in indices of functional and structural BMEC viability. The potential applications and the value of such an experimental approach are discussed.

Dapsone-induced methemoglobinemia: a primer for clinicians

OBJECTIVE

To present a comprehensive review of dapsone-induced methemoglobinemia and its management.

DATA SOURCES

Literature retrieval was accessed through MEDLINE (1966-March 2011), Cochrane Library, and EMBASE, using the terms dapsone and methemoglobinemia.

STUDY SELECTION AND DATA EXTRACTION

All case reports, small case series, and randomized controlled trials published in English were evaluated. Because of the absence of comprehensive updates on this topic since 1996, publications between 1997 and March 2011 were included in this review.

DATA SYNTHESIS

Between 1997 and March 2011, the majority of publications describing methemoglobinemia associated with dapsone use reported this adverse effect at therapeutic doses. Excluding overdose situations, 18 described symptomatic dapsone-associated methemoglobinemia and clinical presentation ranging from cyanosis to dyspnea. In almost all of the accounts, patients had a concurrent event such as anemia or pneumonia, suggesting an interplay between these comorbidities and the onset of symptomatic methemoglobinemia. Delayed hemolytic anemia was seen in patients with high methemoglobin levels at presentation. Management in most cases consisted of administration of methylene blue. Overall, most reports described a successful outcome, and no mortality resulted from methemoglobinemia associated with therapeutic use.

CONCLUSIONS

Clinicians should recognize methemoglobinemia as an adverse effect associated with dapsone use and the potential factors that precipitate it. They should also know how to promptly and effectively manage this event.

Cytochrome P450-dependent toxicity of dapsone in human erythrocytes

The most prominent adverse effects seen during treatment with dapsone, an antibacterial and antiprotozoal agent, are hemolysis and methemoglobinemia. An in vitro microsomal/cytochrome P(450) (CYP)-linked assay, which allows reactive metabolites generated in situ to react with the co-incubated human erythrocytes, was employed to profile CYP isoforms responsible for hemotoxicity of dapsone. Dapsone caused a robust generation of methemoglobin in human erythrocytes in the presence of human/mouse liver microsomes, which indicates contribution of CYP-mediated metabolism for hemotoxicity. The highest methemoglobin formation with dapsone was observed with CYP2C19, with minor contributions from CYP2B6, CYP2D6 and CYP3A4. Cimetidine and chloramphenicol completely abrogated methemoglobin generation by dapsone, thus confirming a predominant contribution of CYP2C19. The results provide useful insights into CYP-dependent hemotoxicity of dapsone in human erythrocytes.

Studies on the toxicity and efficacy of some ester analogues of dapsone in vitro using rat and human tissues

The toxicity and efficacy of a series of 13 anti-tubercular sulphone esters has been evaluated using human and rat tissues. The toxicity studies involved comparison of the esters' ability to generate rat microsomally mediated NADPH-dependent methaemoglobin with that of dapsone. All the compounds formed significantly less methaemoglobin in the 1 compartment studies compared with dapsone itself. The ethyl, propyl, 3-methyl-butyl cyclopentyl esters and the carboxy parent derivative all yielded less than 5% of the methaemoglobin generated by dapsone. The 3-nitro benzoic acid ethyl and propyl esters generated 30 and 25% of dapsone's methaemoglobin formation. A similar effect was seen in the 2 compartment system, except for the butyl ester, which yielded similar haemoglobin oxidation to dapsone. The low toxicity ethyl and propyl esters, were also low in toxicity using human liver microsomes, producing less than 30% of the dapsone mediated methaemoglobin. All the compounds except the benzoic acid parent were superior to dapsone in terms of suppression of human neutrophil respiratory burst using a lucigenin-based chemiluminescence assay. The most potent derivatives were the phenyl, propyl and 3-nitro benzoic acid ethyl esters, which were between two- and threefold more potent compared with dapsone in arresting the respiratory burst. Overall, the ethyl ester showed the best combination of low toxicity in the rat and human microsomal systems and its IC(50) was approximately 40% lower than that of dapsone in neutrophil respiratory burst inhibition. These compounds indicate some promise for future development in their superior anti-inflammatory capability and lower toxicity compared with the parent sulphone, dapsone.

Bioactivation of the cyanide antidote 4-aminopropiophenone (4-PAPP) by human and rat hepatic microsomal enzymes: effect of inhibitors

The bioactivation of the cyanide antidote methaemoglobin former 4-aminopropiophenone (4-PAPP) was studied using rat and human microsomes. With rat liver and NADPH in single and two-compartment systems, dapsone and benzocaine were more potent methaemoglobin generators compared with 4-PAPP. In the single compartment studies, the order of potency of inhibition of 4-PAPP-mediated methaemoglobin formation was cimetidine (1.5 mM)>isoniazid (500 μM)/diethyldithiocarbamate (DDC, 1 mM)>erythromycin (500 μM). Human liver microsomal activation of 4-PAPP in the two-compartment system was partially inhibited by both DDC and cimetidine. These preliminary studies suggest that 4-PAPP may be metabolised by CYP 2C11, 2E1 and 3A in the rat and CYP 2C, 2E1 and probably 3A4 in man.

Preliminary in vitro toxicological evaluation of a series of 2-pyridylcarboxamidrazone candidate anti-tuberculosis compounds

We have investigated the toxicity of a series of 2-pyridylcarboxamidrazones in vitro using a rat liver metabolism system as well as human erythrocytes and mononuclear leucocytes (MNL) as target cells. Of the seven derivatives and four precursors tested, only minimal (<2.3%) metabolism-mediated methaemoglobin was formed by two analogues. However, one of these, a naphthylidene 2-pyridylcarboxamidrazone derivative (compound III), was also directly toxic to human MNLs. This toxicity was partially attenuated by the rat metabolising system and incubation of diethyldithiocarbamate or cimetidine together with compound III and the rat metabolising system suppressed the metabolism-dependent detoxification. This indicated that cytochrome P-450-mediated biotransformation of compound III was preventing its direct toxicity to the MNL. Of the seven derivatives tested, six were low in toxicity to MNL directly and in the presence of a metabolising system. The two compounds which were the most potent anti-mycobacterially, the dimethylpropyl and dimethylethyl benzylidene amidrazone derivatives, were also the least toxic to MNL and erythrocytes. This amidrazone series has shown promise for future development as antituberculosis drugs.

Comparison of the in vitro cytotoxicity of hydroxylamine metabolites of sulfamethoxazole and dapsone

The differential incidence of adverse drug reactions (ADR) between trimethoprim-sulfamethoxazole and dapsone might be explained, in part, by differences in the inherent toxicity of the hydroxylamine metabolites of sulfamethoxazole and dapsone. To test this hypothesis, the in vitro cytotoxicities of sulfamethoxazole hydroxylamine, dapsone hydroxylamine, and monoacetyldapsone hydroxylamine were compared using peripheral blood mononuclear cells (PBMC) from healthy volunteers. After 3 hr of exposure to hydroxylamine metabolites, PBMC were washed thoroughly to remove residual hydroxylamine, and viability was assessed 16 hr later by determination of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) conversion. A concentration-dependent toxicity was observed with each hydroxylamine metabolite. While dapsone hydroxylamine and monoacetyldapsone hydroxylamine were not significantly different, both showed significantly greater cytotoxic potency than sulfamethoxazole hydroxylamine (P < 0.05). This differential potency was not a function of differential stability in aqueous medium and was maintained over time. The effects of red blood cells (RBC), impermeable RBC "ghosts," and RBC lysate on hydroxylamine-induced cytotoxicity were determined using a two-compartment dialysis system. Amelioration of hydroxylamine-dependent cytotoxicity occurred when RBC were included in PBMC incubations. This apparent detoxifying effect was markedly greater using RBC lysate in comparison with impermeable "ghosts" (P < 0.05). No difference in detoxification was observed between sulfamethoxazole hydroxylamine and monoacetyldapsone hydroxylamine. Differences in the inherent cytotoxicity of their hydroxylamine metabolites do not appear to explain the differential incidence of ADR between trimethoprim-sulfamethoxazole and dapsone.

Bioactivation of benzocaine to a methaemoglobin-forming metabolite by rat and human microsomes in vitro

Benzocaine-mediated methaemoglobin-generation was compared with that of dapsone in vitro. Direct incubation of benzocaine with washed human erythrocytes alone at up to 15 mM did not result in significant methaemoglobin formation (0.4 ± 0.1%). With rat microsomes, dapsone-dependent methaemoglobin formation was almost two-fold that of benzocaine at 30 min (56.5 ± 0.7% vs 31.6 ± 2.4% P < 0.005)). Benzocaine-mediated methaemoglobin formation was significantly reduced in the presence of DDC (diethyldithiocarbamate) at the 10 (P < 0.005) and 20 (P < 0.025) min time points. At 30 min, cimetidine reduced benzocaine-mediated methaemoglobin from 34.4 ± 8.7% to less than 3% (P < 0.005). The methaemoglobin forming capacity of dapsone was significantly inhibited at all three time points by both DDC (P < 0.005) and cimetidine (P < 0.005). Incubation of benzocaine with microsomes from five human livers showed that each liver produced methaemoglobin-forming metabolites. No inhibitory effect was seen with DDC, although cimetidine caused a significant reduction (32.8 ± 12.4% overall) in benzocaine-mediated methaemoglobin formation in the four livers tested.

Preliminary evaluation of the toxicity and efficacy of novel 2,4-diamino-5-benzylpyrimidine-sulphone derivatives using rat and human tissues in vitro

Four novel combined dapsone and trimethoprim analogues, K-120, K-150, K-138 and DRS-506, have been compared with dapsone in their methaemoglobin forming abilities as well as their anti-inflammatory properties using rat and human tissues in vitro. All four compounds formed consistently less methaemoglobin compared with dapsone in both the rat and human microsomes. Using human microsomes from five livers, K-120 was significantly less toxic than the other analogues in three of the five livers (P < 0.01). DRS-506 and K-138 both inhibited the human neutrophil respiratory burst to a significantly greater degree compared with dapsone at 0.5 mM (P < 0.01), while K-120 and K-150 showed no significant effect at 0.5 mM. At 1 mM, DRS-506, K-120 and K-138 were more potent than dapsone (P < 0.01), although K-150 appeared to increase the neutrophil activation. All four analogues caused a significant reduction in neutrophil adhesion to human umbilical vein cells at 0.1 mM. In view of its efficacy and low toxicity, K-120 shows considerable promise for future clinical evaluation.

Studies on the toxicity of analogues of dapsone in-vitro using rat, human and heterologously expressed metabolizing systems

Three metabolizing systems (rat, heterologously expressed CYP3A4 and human liver) were used to evaluate 12 analogues of dapsone (4,4'diaminodiphenylsulphone) in-vitro. Methaemoglobin formation in a two-compartment and cytotoxicity in a single-compartment model were studied using human erythrocytes and neutrophils, respectively, as target cells. In the two-compartment system using rat microsomes as a generating system and methaemoglobin as an endpoint, the least potent methaemoglobin formers tested were the 2-methyl-4-propylamino (AXDD14), 2-hydroxy-4-4'amino (ABDD5) derivatives and a sulphone/trimethoprim derivative (K-130). Dapsone itself, a 2-methoxy-4-ethylamino (W10) and a 2-hydroxyl-4-ethylamino compound (ABDD39) were the most toxic. In the single-compartment cytotoxicity test using rat microsomes, AXDD14 was again among the least toxic, as was a 2-methyl 4-cyclopentyl derivative (AXDD17) and surprisingly ABDD39. The most cytotoxic compounds again included dapsone itself as well as two 2-trifluoromethyl derivatives. The only significant methaemoglobin formation and cytotoxicity shown with the heterologously expressed human CYP 3A4 was with AXDD14, which was extensively activated. Interestingly, metabolism of dapsone was low using the expressed CYP 3A4. In the two-compartment system using human liver microsomes, AXDD14, K-130 and ABDD5 were oxidized to a significantly lesser extent compared with dapsone and these preliminary findings indicate that future development of these compounds may be worthwhile.

Dapsone toxicity: some current perspectives

1. Dapsone is a potent anti-inflammatory and anti-parasitic compound, which is metabolised by cytochrome P-450 to hydroxylamines, which in turn cause methaemoglobinaemia and haemolysis. However, during the process of methaemoglobin formation, erythrocytes are capable of detoxifying the hydroxylamine to the parent drug, which may either reach the tissues to exert a therapeutic effect or return to the liver and be re-oxidised in a form of systemic cycling. This glutathione-dependent effect, combined with the un-ionised state of the drug at physiological pH, may contribute to its efficacy. 2. Paradoxically, other aspects of the glutathione-dependent cycling of the hydroxylamine metabolite may contribute to the major adverse reaction of the drug, agranulocytosis. Erythrocytes exposed to the metabolite and repeatedly washed may still release the hydroxylamine in sufficient concentration to kill mononuclear leucocytes in vitro. Thus, erythrocytes may be a conduit for the hydroxylamine to reach the bone marrow to covalently bind to granulocyte precursors, which may trigger an immune response in certain individuals and may lead to the potentially fatal eradication of granulocytes from the circulation. 3. Attempts to increase patient tolerance to dapsone have been most successful using a metabolic inhibitor to reduce hepatic oxidation of the drug to the hydroxylamine. Methaemoglobin formation in the presence of cimetidine was maintained at 30% below control levels for almost 3 mo, and patients' reported side effects such as headache and lethargy were significantly reduced. 4. As clinical application of new and safer dapsone analogues is years away, the use of cimetidine provides an immediate route to increasing patient compliance during dapsone therapy, especially in those maintained on dapsone dosages in excess of 200 mg/day.

Reduction of dapsone hydroxylamine to dapsone during methaemoglobin formation in human erythrocytes in vitro. III: Effect of diabetes

The fate of dapsone hydroxylamine has been investigated in diabetic and normal human erythrocytes. In erythrocytes from four type 1 (insulin dependent) diabetic subjects, there was a significant decrease in dapsone hydroxylamine-mediated methaemoglobin formation compared with cells drawn from normal individuals (P < 0.01). However, the ability of the diabetic cells to detoxify the hydroxylamine to dapsone was not correspondingly reduced and was not different to normal cells. The initial rate of the accelerating effect of diethyl dithiocarbamate (DDC) on hydroxylamine-mediated methaemoglobin and dapsone formation was significantly reduced in diabetic compared with normal cells. There was no significant difference in hydroxylamine-dependent methaemoglobin formation between diabetic erythrocytes pretreated with either statil or sorbinil and untreated diabetic cells. Dapsone recovery in diabetic erythrocytes incubated with statil was not significantly different from statil-free incubations. However, in the presence of sorbinil, there was a marked reduction in dapsone formation at all four time points, (P < 0.001 at 15 min). Mean measured levels of glutathione did not differ significantly between the normal (380 +/- 30.9 mg/L; N = 8) and diabetic (349 +/- 58.7 mg/L; N = 8) volunteers. In summary, although diabetic erythrocytes were less sensitive to the effect of dapsone hydroxylamine-mediated methaemoglobin formation in comparison with normal cells, glutathione-dependent hydroxylamine reduction to dapsone was unaffected.

Reduction of dapsone hydroxylamine to dapsone during methaemoglobin formation in human erythrocytes in vitro. IV: Implications for the development of agranulocytosis

We have studied the efflux of dapsone hydroxylamine from normal and diabetic erythrocytes by the use of a two-compartment (1 and 2) in vitro dialysis system, in order to model the in vivo blood supply to the bone marrow. When both types of erythrocytes were dialysed against mononuclear leucocytes, the hydroxylamine crossed the membrane and caused significantly greater white cell death compared with dialysis of leucocytes against untreated erythrocytes. However, in the case of both normal and diabetic cells, the presence of the glutathione depletor diethyl maleate (DEM) caused a marked reduction in movement of hydroxylamine from compartment 1 to 2. Diethyl dithiocarbamate (DDC), a methaemoglobin accelerant, caused a marked reduction in movement of hydroxylamine from erythrocytes (diabetic and normal) in compartment 1 to 2 which led to a significant reduction in white cell death compared with the absence of DDC (18.3 +/- 5.5 vs 34.8 +/- 8.1%, P < 0.05). Dapsone recovery from compartment 1 rose significantly in the presence of DDC compared with control in both erythrocyte types. In contrast, recovery of dapsone from normal erythrocytes incubated in compartment 1 was significantly reduced by the presence of DEM compared with control, although there was no difference between control and DEM-treated diabetic cells. Dapsone analysis in compartment 2 revealed a significant increase in dapsone recovery in both diabetic (11.3 +/- 1.1%) and normal (11.9 +/- 1.1%) erythrocytes in the presence of DDC compared with diabetic (3.3 +/- 0.4%) and normal control (4.8 +/- 2.0%, P < 0.001). The presence of DEM in compartment 1 caused a significant fall in dapsone recovery in compartment 2 (3.7 +/- 0.26) compared with control (4.7 +/- 0.36%, P < 0.05). Hence, dapsone hydroxylamine is capable of leeching out of normal and diabetic erythrocytes, traversing a semipermeable membrane and causing toxicity to human mononucleocyte cells in vitro. This process may be one of the first stages in immune-mediated agranulocytosis.