Photoreactivity of biologically active compounds: XI. Primaquine and metabolites as radical inducers

doi:10.1016/S0928-0987(97)00268-6

European Journal of Pharmaceutical Sciences

Volume 5, Issue 3, 1 May 1997, Pages 139-146

https://doi.org/10.1016/S0928-0987(97)00268-6 Get rights and content

Abstract

Reduction of ferricytochrome C and oxidation of haemoglobin was used to examine redox properties of primaquine, metabolites and photodegradation products of the drug. The influence of oxygen radicals (O₂·− and OH·) were studied by the addition of oxygen radical scavengers. Photodecomposition of primaquine (80 mW/cm², xenon lamp, 290–800 nm) prior to dark-incubation resulted in a substantial accelerated drug-induced O₂·− formation and haemoglobin oxidation. Formation of OH· (dark reaction) could be detected after photochemical degradation of primaquine. In the presence of erythrocytes the formation of oxygen radicals induced by the photodecomposition products was even more pronounced. A high oxygen content in the medium during irradiation accelerated the photodecomposition-rate of primaquine. The metabolite 6-desmethyl primaquine was a more potent O₂·− producer and haemoglobin oxidizer than primaquine (dark reactions). During irradiation (80 mW/cm², 290–800 nm) primaquine formed more O₂⋅− and produced a detectable level of OH· compared to the dark reactions.

Introduction

Primaquine is an 8-aminoquinoline with antimalarial activity. The drug eliminates persistent liver forms of Plasmodium ovale and P. vivax. Primaquine has no effect on the erythrocytic stages of Plasmodia unless toxic doses are administered. Severe adverse effects (haemolysis and methaemoglobinaemia) are observed after administration of primaquine, manifested particularly in patients with glucose-6-phosphate dehydrogenase deficiency (WHO, 1988). This enzyme is part of the anti-oxidative defence system, protecting the erythrocytes against peroxidative reactions (Chiu et al., 1989). Thus primaquine is not suitable for general malaria prophylaxis, although it might have to be given prophylactically together with a blood schizontocide (e.g. chloroquine) in areas where P. ovale and P. vivax are endemic (Reynolds, 1989).

Primaquine absorbs light in the UV-visible region of the spectrum. Light-exposure of the compound in an aqueous oxygen containing medium causes various structural changes in the side chain of the molecule. Eight major and several minor decomposition products are formed (Kristensen et al., 1993). Primaquine acts as a photosensitizer in vitro, inducing photohaemolysis and photopolymerization of proteins (Kristensen et al., 1994, Kristensen et al., 1995). The compound oxidizes haemoglobin and NADPH by formation of superoxide, hydroxyl radicals and hydrogen peroxide in vitro (Summerfield and Tudhope, 1978, Thornalley et al., 1983).

The haematologic adverse effects caused by primaquine might be due to the formation of radicals in vivo. Radical formation is further important with respect to drug stability and formation of degradation products which may be toxic. This work was undertaken to obtain further information on the in vitro formation of radicals from primaquine during light exposure and from the photodecomposition products and most important metabolites of primaquine in the absence of light.

Section snippets

Materials

Primaquine diphosphate (PQ; >99% pure, Aldrich, Germany), ferricytochrome C (cytC; from Bovine heart, 99% pure, ferrocytochrome C content <5%), superoxide dismutase (SOD; from Bovine erythrocytes, 98% pure), D-mannitol (MAN), 6-methoxy quinoline (6MQ), 8-amino quinoline (8AQ) and quinoline (QUI; 98% pure), all Sigma, USA, were used as received. The metabolites of PQ (6-desmethyl primaquine hydrobromide (DPQ), carboxy primaquine (CPQ), N-acethyl primaquine (APQ) and 8-amino-6-methoxy quinoline

Results and discussion

The structural formulas of PQ and the derivatives and metabolites of the drug are illustrated in Fig. 1.

Each result (Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6 and the results given in the text) is the mean of two measurements. 74% of the parallels deviate less than 10% from the mean, 16% deviate 10–20% and 10% deviate more than 20% from the mean.

Conclusion

One (or several) of the photochemical degradation products formed during irradiation of PQ is a more potent inducer of oxygen radicals (O₂·− and OH·) and a more powerful Hb-oxidant than the parent drug in the absence of light. The oxygen content in the sample affects the photodecomposition-rate of PQ. Hence, PQ exposed to light seems to form decomposition product(s) more toxic than the drug itself. The presence of RBC was observed to accelerate the O₂·− and OH· production induced by the

Acknowledgements

The authors thank Henrik Schultz, Weifa A/S, Norway, and Professor J.D. McChesney, University of Mississippi, USA, for providing the HPLC methode and the metabolites of PQ, respectively, John Vedde, Institute of Chemistry, University of Oslo, Norway, for assistance with the MS analysis, and Anne-Lise Orsteen, Institute of Pharmacy, University of Oslo, Norway, for drawing figures.

References (16)

Baty, J.D., Price Evans, D.A. and Robinson, P.A. (1975) The identification of 6-methoxy-8-aminoquinoline as a...
Bisby, R.H. (1988) One-electron reduction of the antimalarial drug primaquine, studied by pulse radiolysis. Free Radic....
Caughey, W.S. and Watkins, J.A. (1985) Oxy radical and peroxide formation by hemoglobin and myoglobin. In Greenwald,...
Chiu, D., Kuypers, F. and Lubin, B. (1989) Lipid peroxidation in human red cells. Semin. Hematol. 26,...
Fridovich, I. (1985) Cytochrome c. In Greenwald, R.A. (Ed.), CRC Handbook of Methods for Oxygen Radical Research, CRC...
Halliwell, B. and Gutteridge, J.M.C. (1985) Free Radicals in Biology and Medicine, Clarendon Press,...
Koppenol, W.H. and Butler, J. (1984) The radiation chemistry of cytochrome c. Isr. J. Chem. 24,...
Kristensen, S., Grislingaas, A-L., Greenhill, J.V., Skjetne, T., Karlsen J. and Tønnesen, H.H. (1993) Photochemical...

There are more references available in the full text version of this article.

Cited by (12)

Photoreactivity of biologically active compounds. XIX: Excited states and free radicals from the antimalarial drug primaquine
2009, Journal of Photochemistry and Photobiology B: Biology
Citation Excerpt :
irradiation in the presence of the quencher. Hence free radical reactions also contribute to photodegradation of primaquine, as postulated earlier by a series of scavenging experiments [2,4,5]. Formation and reactivity of the monoprotonated cation radical is expected to play an essential part in the initial photochemical degradation of primaquine at physiological pH, as illustrated in Scheme 2.
The formation and reactivity of excited states and free radicals from primaquine, a drug used in the treatment of malaria, was studied in order to evaluate the primary photochemical reaction mechanisms. The excited primaquine triplet was not detected, but is likely to be formed with a short lifetime (<50 ns) and with a triplet energy <250 kJ/mol as the drug is an efficient quencher of the fenbufen triplet and the biphenyl triplet, and forms $^{1} O_{2}$ by laser flash photolysis $(^{PQ} Φ_{Δ} = 0.025)$ . Primaquine (PQ) exists as the monocation $({PQH}^{+})$ in aqueous solution at physiological pH. ${PQH}^{+}$ photoionises by a biphotonic process and also forms the monoprotonated cation radical $({PQH}^{2 +})$ by one electron oxidation by ${HO}^{}$ (k_q = 6.6 × 10⁹ M⁻¹ s⁻¹) and ${Br}_{2}^{-}$ (k_q = 4.7 × 10⁹ M⁻¹ s⁻¹) at physiological pH, detected as a long-lived transient decaying essentially by a second order process (k₂ = 7.4 × 10⁸ M⁻¹ s⁻¹). ${PQH}^{2 +}$ is scavenged by O₂, although at a limited rate (k_q = 1.0 × 10⁶ M⁻¹ s⁻¹). The reduction potential (E°) of ${PQH}^{2 +} / {PQH}^{+}$ is < +1015 mV, as measured versus tryptophan ( ${TRP}^{} / TRPH$ ). Primaquine also forms ${PQH}^{2 +}$ at pH 2.4, by one electron oxidation by ${Br}_{2}^{-}$ and proton loss (k_q = 2.7 × 10⁹ M⁻¹ s⁻¹). The non-protonated cation radical ( ${PQ}^{+}$ ) is formed during one electron oxidation with ${Br}_{2}^{-}$ at alkaline conditions (k_q = 4.2 × 10⁹ M⁻¹ s⁻¹ at pH 10.8). The estimated pK_a-value of ${PQH}^{2 +} / {PQ}^{+}$ is pK_a ∼ 7–8. Primaquine is not a scavenger of $O_{2}^{-}$ at physiological pH. Thus self-sensitization by $O_{2}^{-}$ is eliminated as a degradation pathway in the photochemical reactions. Impurities in the raw material and photochemical degradation products initiate photosensitized degradation of primaquine in deuterium oxide, prevented by addition of the $^{1} O_{2}$ quencher sodium azide. Photosensitized degradation by formation of $^{1} O_{2}$ is thus important for the initial photochemical decomposition of primaquine, which also proceeds by free radical reactions. Formation of ${PQH}^{2 +}$ is expected to play an essential part in the photochemical degradation process in a neutral, aqueous medium.
Reaction of singlet molecular oxygen, O<inf>2</inf>(<sup>1</sup> Δ<inf>g</inf>), with the Cinchona tree alkaloids: Effect of absolute configuration on the total rate constant
2005, Journal of Photochemistry and Photobiology A: Chemistry
Detection of O₂(¹Δ_g) emission, λ_max = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, k_T, and the reactive reaction rate constant, k_R, for the reaction between singlet oxygen and the Cinchona tree alkaloids, cinchonidine, cinchonine, quinine and quinidine in several solvents. In most solvents, the k_T values were close to 10⁷ M⁻¹ s⁻¹, indicating that these compounds are good singlet oxygen quenchers. The reactive rate constants are smaller than 10⁴ M⁻¹ s⁻¹, implying that quenching is essentially a physical process. The analysis of solvent effect on k_T by using LSER equations indicates that singlet oxygen deactivation by these drugs is accelerated by solvents with large π^* and β values, being inhibited by hydrogen bond donor (HBD) solvents. Correlations employing theoretical solvent parameters, TLSER, give similar results. These data support the formation of an exciplex with charge transfer character, resulting from the singlet oxygen electrophilic attack on the quinuclidine moiety nitrogen. In most solvents, cinchonidine is more reactive than cinchonine and quinine is more reactive than quinidine although reactivity differences are small and only in a few solvents k_T values of the S,R-isomer are about twice than those of R,S-isomer. The higher reactivity of S,R-isomers in these solvents is explained by the geometrically favorable intra-exciplex stabilizing interaction between the non-bonded pernitrone oxygen and the hydrogen of the hydroxyl substituent at C(9).
Solvent effects on reactions of singlet molecular oxygen, O<inf>2</inf>(<sup>1</sup>Δ<inf>g</inf>), with antimalarial drugs
2004, Journal of Photochemistry and Photobiology A: Chemistry
Detection of O₂( $^{1} Δ_{g}$ ) emission, λ_max=1270 nm, following laser excitation and steady-state methods were employed to measure total reaction rate constants, k_T, for the reaction between singlet oxygen and the antimalarial drugs quinine (QU), quinacrine (QC), chloroquine (CQ) and amodiaquine (AQ) in several solvents. Values for k_T range from 0.45±0.03×10⁷ M⁻¹ s⁻¹ for AQ in benzene to 25.1±0.88×10⁷ M⁻¹ s⁻¹ for CQ in N,N-dimethylformamide. Analysis of solvent effect on k_T for QU, QC, and CQ by using the LSER formalism indicates that singlet oxygen deactivation by these drugs is accelerated by solvents with large π^∗ values and hydrogen bond acceptor (HBA) properties and is inhibited by hydrogen bond donors (HBD) solvents. This result support the formation of an exciplex intermediate of charge transfer character, as proposed for reactions of tertiary amines with singlet oxygen, process largely governed by physical quenching. AQ behaves in a different manner. The LSER equation for this drug shows that k_T increases in solvents with large π^∗ values and diminishes in HBD solvents. In this case, reaction mechanism probably involves a partially concerted cycloaddition of singlet oxygen to the aminophenolic ring in position 4.
Photosensitizing properties of quinine and synthetic antimalarials
1998, Journal of Photochemistry and Photobiology B: Biology
Quinine, an alkaloid that occurs in the bark of trees of the genus Cinchona, has been used for the treatment of malaria in humans for over 150 years. In 1888 it was reported that quinine was more toxic to plant tissues and frog eggs in the light than in the dark; thus it is probably one of the first pure compounds shown to be a photosensitizer for biological systems. During this century, because of the toxic side effects of quinine and the appearance of quinine-resistant malarial strains, a search was begun to identify synthetic antimalarial compounds with improved properties. A number have been identified and are now in widespread use; but, like quinine, most of these are also photosensitizers. Because of the very large numbers of patients receiving antimalarials, many studies have been made of the photophysical, photochemical and photosensitizing properties of quinine and several of the most commonly used synthetic antimalarials (chloroquine, primaquine, quinacrine and mefloquine). The results of these studies are summarized in this review. Most antimalarials photosensitize in part by the generation of singlet oxygen, although free radical pathways may also be involved. The carcinogenic and photocarcinogenic properties of antimalarials and related compounds are briefly surveyed.
Stability
2023, Practical Pharmaceutics: An International Guideline for the Preparation, Care and Use of Medicinal Products, Second Edition
Electrospray ionization mass spectrometry as a valuable tool in the characterization of novel primaquine peptidomimetic derivatives
2009, European Journal of Mass Spectrometry

View all citing articles on Scopus

View full text