Introduction

Falciparum malaria is a mass killer that went out of control. The drug treatments for this potentially lethal infection that have been most widely recommended and provided over the past 50 years (i.e., chloroquine and sulfadoxine–pyrimethamine) no longer work in most tropical countries. Resistance to these drugs emerged in Asia and South America and spread to Africa. Replacing the failing chloroquine and sulfadoxine–pyrimethamine with effective drugs necessitate the artesunate invention ₁ , ₂

Pregnant women are a high-risk group in malaria attack, being more susceptible and likely to develop anemia, and if non-immune, are more likely to develop complications. Birth-weight is consistently reduced by malaria. Therefore, pregnant women desperately need effective and safe antimalarial treatments. The main concern surrounding the general deployment of the Artemisinin-based Combination Therapy (ACTs) is their safety in the first trimester of pregnancy ₃ , ₄ , ₅ , ₆ . Work by Chinese scientists in rodents and rabbits conducted in the 1970s indicated that early pregnancy exposure could induce fetal resorption. Recent reproductive toxicity studies have confirmed that this is a class effect of the compounds and is seen in all experimental animal species studied. It results from a specific inhibition of fetal erythropoeisis. Fetal resorption would result in early pregnancy loss. Much more worrying is the potential to cause developmental abnormality. In rodents and rabbits at doses close to human therapeutic doses, artemisinins given in a critical period in the early stage of gestation, may also cause limb deformation. In primates, doses of 12–30 mg/kg daily given continuously between days 20 – 50 postcoitum which is equivalent to 20–56 days in human pregnancy caused fetal resorption and mild long bone shortening, but no abnormalities were seen ₇ .

In earlier studies, artesunate, an artemisinin antimalarial, had been reportedly embryolethal and teratogenic in rats, with the most sensitive days being 10 and 11 postcoitum ₅ . Pregnant rats were administered a single oral dose of 17 mg/kg artesunate on days 10-11 and conceptuses were evaluated through day 14. Among other defects observed, delay in limb and tail development occurred by day 13. While embryos were viable through day 13, about 77% of embryos had died by day 14, presumably due to hypoxia and/or cardiac abnormalities. The same adverse effects were seen in the brain ₈ , ₉ and in a similar work to compare the developmental toxicity of structurally related artemisinins, dihdyroartemisinin, artemether, and arteether to that of artesunate after oral administration to rats ₆

On the other hand, bones are rigid organs that form part of the endoskeleton of vertebrates. Bones function to move, support and protect the body; produce red and white blood cells and store minerals. The process of bone formation occurs in three stages, orchestrated by specialized bone cells that secrete and absorb materials as needed. First, a soft cartilage-based foundation is laid, upon which mature bone will solidify. Then, minerals containing calcium and phosphate are deposited throughout the foundation, creating a framework for the bone. Finally, this raw material is sculpted and hardened into bone. Errors in this process can result in developmental defects and bone diseases ₁₀ , ₁₁ . The present work examines the embryotoxic effects of artesunate on the developing bones.

Materials And Methods

Procurement of animals

Administration of drug

Sacrifice of animals

Procedures for bone mineral analysis

Results

Assessment of bone calcification

Assessment of foetal rat morphology

Assessment of bone mineral values

Calcium and Phosphorus are expressed as milligram per gram dry bone weights. In the group C, the calcium content was low through out the foetal age. Likewise the phosphorus, the levels apparently plateaued through the gestational days and were significantly lower than the control and group B (Table 3). Calcium level was relatively higher in the control and group B foetuses than in the group C through out the gestational days. Phosphorus contents were higher in the control than group B rats. In the group C, the mineral levels remained relatively lowest throughout the foetal days.

Figure 1

Table 1.1 The earliest days of calcification (Ö) in the skull bone of Wistar rats’ foetuses monitored from day 12 to day 21 of gestation (foetuses, n = 6/group/day)

Figure 2

Table 1.2 The earliest days of calcification (Ö) in the axial bone of Wistar rats’ foetuses monitored from day 12 to day 21 of gestation (foetuses, n = 6/group/day)

Figure 3

Figure 4

Table 1.3 The earliest days of calcification (Ö) in the appendicular bones of Wistar rat foetuses monitored from day 12 to day 21 of gestation (foetuses, n = 6/group/day)

Figure 5

Figure 6

Table 2. Percentages of Surviving foetuses of Wistar rats with malformations

Figure 7

Table 3. Analysis of bone mineral values (mg/g, from day 12 – 21 of gestation) in the Wistar rats’ foetuses

Figure 8

Fig. 1: Skeletal defects in the group B rat indicating delay ossification in the caudal bone-(DC); tarsal bone-(DT) and occipital bones-(DO). Alizarin red S stains (x4)

Figure 9

Fig. 2: Skeletal defects in the group C rat indicating delay ossification in the tarsals bone (DT) and thoracic vertebra-(DV). Alizarin red S stains (x4)

Discussion

Artesunate is a potent blood schizonticide agent for plasmodium falciparum ₁₅ . It is effective against Plasmodium falciparum resistant to all other antimalarial drugs. It does not have hypnozoiticidal activity. Artesunate has been reported to clear fever in patients with severe falciparum malaria 16 - 25 hours after parenteral administration. Artemisinin and its derivatives inhibit erythropoiesis in the early foetus, this could possibly explain the paleness, wrinkle skin observed and fetal resorption seen in the experimental animals. In its malarial combat quest, artesunate binds tightly to parasitized erythrocyte membranes ₁₆ . The functional group responsible for antimalarial activity of artesunate is endoperoxide bond. Release of an active oxygen species from this bond kills the malaria parasite if accumulated in the erythrocytic cells. Artesunate has demonstrated the fastest clearance of all anti-malarials currently used and acts primarily on the trophozite phase, thus preventing progression of the malaria disease. It is converted to active metabolite dihydroartemesinin that then inhibits the sarcoplasmic/endoplasmic reticulum Calcium ATPase encoded by P. falciparum, ₂₁₇ . The mechanisms of its osteo-toxicity could not yet be ascertain presently; but it is possible that, like ethanol, artesunate could facilitate the action of the calcification inhibitors ₁₃ , that is, a family of inorganic pyrophosphatases, phosphonates and diphosphonates; these act normally to prevent calcium deposits from forming on soft tissues ₁₈ . Although artesunate produced lesser assaults compared to other drugs, this work is indicative and confirms the adverse effect profiles of the artemisinin-based treatments, its toxicity cum teratogenicity ₆₁₉ , ₁₃ , ₂₀ , ₂₁ , ₂₂ , ₂₃ , hence, a caution in its use particularly in early pregnancy ₁₇ . Such fears of its toxicity and a possible emergence of resistance of the malaria parasite to artesunate had of recent posed a threat to the use of this much preferred drug. Hence, Artemisinin-based combination treatments (ACTs) are now generally accepted as the best treatments for uncomplicated falciparum malaria ₁₇ , ₂₄ . The combination – depending on the location and prevalence of malaria parasites could be: artesunate–mefloquine, artemether–lumefantrine, and dihydroartemisinin–piperaquine. They are rapidly and reliably effective. Efficacy is determined by the drug partnering the artemisinin derivative. Artesunate–sulfadoxine–pyrimethamine and artesunate–amodiaquine are effective in some areas, but in other areas, resistance to the partner precludes their use. There is still uncertainty over the safety of artemisinin derivatives in the first trimester of pregnancy when they should not be used, unless there are no effective alternatives ₂₅ . Most malaria endemic countries have now adopted artemisinin-based combination treatments as first-line treatment of falciparum malaria, but in most of these, only a minority of the patients that need artemisinin-based combination treatments actually receive them. Because these drugs have not been evaluated extensively in early pregnancy in humans, they should be avoided in patients in the first trimester of pregnancy with uncomplicated malaria until more information is available. There is no evidence for adverse effects on the foetus exposed in the second and third trimesters, when these drugs are recommended depending on the safety profile of the partnering drug ₁₇ .