Abstract

Iron storage disease, or hemochromatosis, has been documented in a number of exotic and domestic species, as well as in man. Various avian species are affected by this condition, most notably mynahs, toucans, birds of paradise, starlings, and hornbills.^2,3,7,8 It is characterized by excessive accumulation of iron in parenchymal tissues with associated functional or morphologic damage. Birds with iron storage disease may die with no premonitory signs or may succumb to hepatic or myocardial failure.^2,7,8

Early diagnosis and treatment of hemochromatosis is essential, as the degree of iron overload has prognostic implications. Therapeutic options consist of phlebotomy or iron chelation therapy.^1,6 Phlebotomy has been employed in avian species, however, difficulties arise due to the small size of some patients, the stress of frequent handling, and the uncertainty of the maximum safe volume of blood that can be removed at frequent intervals in a potentially compromised patient.⁸ Currently deferiprone (L1, Apotex Inc. Weston, Ontario, Canada), which is administered orally, and deferoxamine (DFO, Desferal®, Novartis Pharmaceuticals, Dorval, Quebec, Canada), which must be administered parenterally, are the only two iron chelators available for treating the disease.^1,6 Neither drug has been studied scientifically in avian species, although there have been two case reports of successful iron chelation therapy with deferoxamine.^2,7

We conducted a multi-phase scientific investigation into the pharmacokinetic and clinical applicability of deferiprone for the treatment of iron overload in birds. The objectives of the phase of our research reported here were: (1) to evaluate the efficacy of deferiprone to decrease hepatic iron stores in two species after inducing experimental hemosiderosis, and (2) to assess for clinical, toxicologic or pathologic abnormalities associated with drug administration.

Materials and Methods

White leghorn chickens (Gallus forma domestica) and domestic king pigeons (Columba livia) were used, to allow interspecific comparisons of the actions of deferiprone. Experimental design was identical for each species. Birds were randomly allocated to one of three groups of 10 birds (Control [NIL-C], iron loaded-deferiprone treated [IL-DFP] or iron loaded [IL]). All birds were banded, weighed and blood sampled to establish baseline hematologic and biochemical values, and plasma iron parameters (iron levels, total iron binding capacity [TIBC], unbound iron binding capacity [UIBC], and transferrin saturation levels [TS%]).

The birds in the IL-DFP and IL group were administered intravenous iron dextran at 25 mg/kg to induce hemosiderosis. The IL-DFP group was gavaged with a deferiprone suspension at a dose of approximately 50 mg/kg twice daily. The IL group did not receive any deferiprone while the NIL-C group received neither iron dextran nor deferiprone.

The duration of treatment was 30 days. Five birds in each group were randomly selected for weekly assessment of plasma iron parameters. Biochemical and hematologic parameters were assessed in these birds at the midpoint during the treatment period and at the end. Plasma zinc, copper and magnesium levels were assessed at the endpoint of the study. Birds were also weighed on a weekly basis to monitor body weight and adjust the deferiprone dose. In the leghorns, egg production was also monitored.

At the conclusion of the trial, the birds were euthanatized, necropsied and tissues were collected for histopathologic examination (hematoxylin-eosin and Perl’s staining). The livers were weighed, and then portions submitted for quantitative determination of iron stores.

Results

There were no drug-associated mortalities in the pigeons, while three chickens died in the deferiprone treatment group midway through the study. Although there were no significant differences in food intake, there were differences in weight gain in the IL-DFP group compared with both the IL and NIL-C groups for both species (Table 1). After the morning treatment, birds being treated with deferiprone did not initiate feeding behavior as quickly as the non-treated groups, while there were no observed differences in feeding behavior among the three groups after the evening treatment. The most significant clinical finding in the deferiprone treatment group in both species was the production of rust-colored urates indicative of renal excretion of Fe-deferiprone complexes.

There were no clinically significant alterations in the hematologic or serum biochemical values in either the pigeon or chicken trial. A decrease in plasma zinc levels was observed in the deferiprone treated birds of both species, while there were no significant changes in plasma copper or magnesium levels compared to the IL or NIL-C groups (Table 2).

The plasma iron parameters are summarized in Table 3. In both species, there was a marked reduction in hepatic iron concentration in the IL-DFP groups compared with the IL groups that were not treated with the drug. In the pigeons, the hepatic iron concentration in the deferiprone treated group was even lower than the NIL-C control group (Table 4). Blood collection did not affect endpoint hepatic iron levels. Histopathology results are pending.

Table 1. Average weekly change in bodyweight

^aIron loaded-deferiprone tx.
^bIron loaded.
^cControl.

Table 2. Mean plasma zinc concentrations (mg/dL)

^aIron loaded-deferiprone tx.
^bIron loaded.
^cControl.

Table 3. Mean plasma iron levels, TIBC, UIBC and transferrin saturation for 30-day trial period

^aIron loaded-deferiprone tx.
^bIron loaded.
^cControl

Table 4. Mean hepatic iron concentration after 30-day trial period (µg of iron/gram of liver-dry weight)

^aIron loaded-deferiprone tx.
^bIron loaded.
^cControl

Discussion

This study demonstrates the clinical applicability of the orally active iron chelator deferiprone for the treatment of iron overload in avian species. When administered at a dose of 50 mg/kg orally twice daily the hemosiderotic state induced by experimental iron loading was eliminated within the 30-day treatment period. The drug can be administered with food since only the rate, not the extent, of absorption is affected by food consumption.^1,6

No statistically or biologically significant alterations occurred in the hematologic and biochemical parameters measured in this study. Our study concurred with others that plasma iron concentrations and transferrin saturation (TS%) were a poor indication of total body and hepatic iron status as indicated by IL and NIL-C groups.^2,9 However, the decrease in TS% in the IL-DFP groups correlates well with the mechanism of action of drug, which mobilizes iron from transferrin, as well as free iron and iron from ferritin and hemosiderin. The increase in UIBC is most likely a reflection of the formation of deferiprone-iron complexes.⁶

Although iron chelation was successful, administration of deferiprone was not without side effects. Deferiprone has a strong affinity for iron, but also binds with zinc, copper and aluminum.^1,6 Further diagnostics, including histopathology, tissue culture, and deferiprone plasma levels, are being carried out at the time of this abstract to investigate the cause of death in the three chickens. There was no significant difference in copper levels among the three groups in either the chickens or the pigeons; however, a significant decrease in plasma zinc levels was noted in both species. Zinc is one of the most metabolically active trace minerals, however, storage pools are small, and zinc deficiency can be induced rapidly in some species of animals. Zinc deficiency is responsible for decreased appetite, cyclic feeding, and reduced weight gain, and could be a plausible explanation for the decreased weight gain in the deferiprone treated groups in this study.^4,5 Zinc is also an important component of other physiologic processes including immunocompetence, electrolyte balance, fertility, cell replication and growth, and feathering.^4,5 Zinc levels should be monitored closely while birds are being treated with deferiprone, and supplemental dietary zinc may be indicated.

Gastrointestinal disturbances such as anorexia, nausea, vomiting and diarrhea have been reported in human patients on the drug.^1,6 Although vomiting and diarrhea were not noted in the deferiprone treatment groups, the slower initiation of feeding activity may be related to transient gastrointestinal upset, especially if the drug is given in the absence of ingesta in the upper gastrointestinal tract. There was no evidence of arthropathy in the treated pigeons or chickens, as has been reported in up to 39% of human patients in clinical trials.¹

In conclusion, deferiprone is a promising orally active iron chelator for the treatment of iron overload in birds. The drug may have potential for use in preventing hemochromatosis. Further clinical studies in affected species are needed to determine the most effective way to use this drug while minimizing the side effects associated with administration.

Acknowledgments

The Toronto Zoo Foundation and the Ontario Veterinary College’s Pet Trust Fund funded this project. In addition, we are grateful to Apotex Inc. for providing the deferiprone and other generous support, and we thank Dr. Michael Spino, Angelo Tesoro, Dr. Fernando Tricta, and Dr. Jake Thiessen of Apotex Inc. for their contributions to the project. Our gratitude is extended to the keepers and veterinary technicians in the Animal Health Center at the Toronto Zoo for their assistance with animal care, and to the veterinary technicians for their assistance with the project. We thank Ann Bell of the Arkell Research Station, University of Guelph, and Dr. Bruce Hunter for their contributions to the project, and the staff of the Animal Health Laboratory, University of Guelph for their efficient processing of samples. This work was completed as partial fulfillment of the requirements for a Doctor of Veterinary Science graduate degree by the senior author.

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8.  Worell, A.B. 1991. Phlebotomy for treatment of hemochromatosis in two sulfur-breasted toucans. Proc. Annu. Conf. Assoc. Avian Vet. Pp. 9–14.

9.  Worell, A.B. 1993. Further investigations in rhamphastids concerning hemochromatosis. Proc. Annu. Conf. Assoc. Avian Vet. Pp. 98–107.