Iron overload is a major life-threatening complication of thalassemia major and other iron-loading anemias treated by regular blood transfusions. Although the clinical manifestations of iron overload may be prevented by desferrioxamine, the only iron-chelating drug in routine clinical use, this treatment requires subcutaneous infusion of desferrioxamine for 12 hours each day. New orally effective iron chelators are urgently needed, and pyridoxal isonicotinoyl hydrazone (PIH), which was first recognized as an effective iron chelator in vitro and subsequently in vivo, shows promise for the treatment of iron overload. More recently, over 40 analogs of PIH were synthesized, and some of them proved to be very potent in mobilizing 59Fe in vitro from 59Fe-labeled cells. In this study, we show that PIH analogs such as pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone (PMBH), pyridoxal m-fluorobenzoyl hydrazone (PFBH), and pyridoxal-2-thiophenecarboxyl hydrazone, compounds previously shown to mobilize iron from cells in vitro, are also effective in vivo. All of these chelators significantly enhanced biliary excretion of iron (measured by atomic absorption spectrophotometry) following their intraperitoneal (IP) and/or oral administration to rats. The most effective was PFBH, which increased iron concentration in the bile about 150-fold, as compared with basal biliary iron concentration, within 1 hour following a single IP dose of 0.2 mmol/kg body weight. In contrast, desferrioxamine increased the biliary iron concentration only 20-fold to 30-fold under the same conditions. Moreover, while control rats excreted ≈ 0.8 μg Fe in 2 hours, treatment with PFBH, PMBH, and desferrioxamine resulted in cumulative excretions of 87, 59, and 22 μg Fe, respectively, in the same period of time. Interestingly, PMBH was also quite effective following gastric administration, resulting in a 6-hour cumulative value of 34 μg Fe. These compounds are nontoxic and are inexpensive and easy to make. Their further evaluation as candidate drugs for the treatment of iron overload is warranted.

DESFERRIOXAMINE (DFO) is the only iron chelator in routine clinical use for the treatment of secondary iron overload, but this drug is very expensive and may cause toxic side effects. Moreover, desferrioxamine treatment involves a slow subcutaneous delivery over a 12-hour period each day, resulting in lack of compliance with the therapy.1-3 Although the new orally active chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1, deferiprone) increases urinary Fe excretion,4,5 clinical trials have shown a number of serious complications with L1 therapy, including agranulocytosis, arthritis, and gastrointestinal side effects.6-11 Moreover, recent long-term clinical trials showed that there is either no overall change in iron stores12 or that mean body iron increases13 in the course of L1-treatment. In fact, tissue iron can reach concentrations associated with iron-induced complications in 95% of patients.13 Hence, there is an urgent need to develop alternative iron chelators that are economical, orally effective, and highly efficient.

Pyridoxal isonicotinoyl hydrazone (PIH), produced by the Schiff base condensation of pyridoxal and isonicotinic acid hydrazide (INH), was initially identified as an effective iron chelator in vitro.14,15 Subsequently, PIH was found to be effective in vivo when given parenterally to mice15 and orally to rats.16-19 The high activity of PIH both in vitro and in vivo14-26 has prompted a clinical trial, where PIH showed no evidence of toxicity and produced significant iron excretion.27 

We have recently synthesized 44 analogues of PIH, which retained the key iron-binding groups, and tested their effect on hepatocyte iron uptake from transferrin, as well as on iron mobilization from intracellular sites of hepatocytes.28 This study identified several PIH analogues, which are relatively simple and inexpensive to synthesize, that are highly effective in blocking 59Fe uptake by hepatocytes and/or mobilizing hepatocyte59Fe. Another study29 confirmed these results and also documented that the compounds do not cause toxic effects when added in effective concentrations to isolated rat hepatocytes incubated in vitro. In the present study, we examined the capacity of these newly identified iron chelators to promote biliary iron excretion following their administration to rats.

Animals.

Female Wistar rats (220 ± 20 g) fed on a standard pellet diet were used. The rats were starved 24 hours before the experiment during which they had free access to deionized water.

Chelators.

The chelators were synthesized by Schiff base condensation between appropriate aldehydes and acid hydrazides, using standard procedures.30 The number codes (Fig 1) for the hydrazones were identical as in our previous reports.24,28 The compounds were characterized with respect to their carbon-hydrogen analysis, melting points, and infra-red and nuclear magnetic resonance spectra.30 The chelators were administered either intraperitoneally (IP) or by gastric gavage at the dose of 0.2 mmol/kg body weight, roughly corresponding to concentrations shown to be effective in in vitro systems.28 29 Solutions of chelators were prepared within 30 minutes or less before administration, as follows: the appropriate amount of chelator was dissolved in a minimum volume (0.3 to 0.5 mL) of 1 mol/L HCl, then adjusted to pH 6 to 7 by addition of Krebs-Henseleit buffer (pH 7.4). The temperature of the solution was kept within the range of 35°C to 37°C. Injected volumes were approximately 1 mL per rat, depending on the body weight.

Fig. 1.

Structures of PIH analogs examined in this study. The number codes are identical to those in previous reports.24 28 

Fig. 1.

Structures of PIH analogs examined in this study. The number codes are identical to those in previous reports.24 28 

Close modal
Experimental procedure.

The bile duct was cannulated using fine tubing (PE-20, Clay-Adams, internal diameter 0.28 mm), which was then subcutaneously conveyed to the dorsal area, exposed extracorporeally, and connected to a small test tube fitted to a jacket that was fixed on the back of the rat. The bile was collected in 12 × 75 mm plastic tubes, which were replaced as needed to allow assessment of the rate of bile flow and the iron content in the bile.31 The animals were kept in metabolic cages and bile samples were collected every hour for 2 hours before and 8 hours after administration of the chelator. Immediately after the collection, the weight of the bile sample was determined, and the samples were kept in a refrigerator until analyzed. The urine was collected for 18 hours before and after the injection of chelator using the method described earlier.31 32 At the end of the experiment, the rats were killed by exsanguination from the heart, and the brains were carefully removed and weighed.

Iron determinations.

All analyses were performed on an AAS-30 Varian spectrophotometer (Varian Techtron Pty, Limited, Mulgrave, Victoria, Australia) equipped with Zeeman's background correction for flameless and deuterium correction for flame technique. The concentration of iron in the bile was determined directly using flameless technique. The content of iron in the urine was determined after extraction of filtration paper with 30 mL of 0.1 mol/L Na-EDTA (flame technique).

Our recent study showed that several hydrazones of pyridoxal,viz those derived from hydrazides of benzoic (#101), p-methoxybenzoic (#107), m-fluorobenzoic (#109), and 2-thio-phenecarboxylic (#115) acids, as well as pyridoxal 2-furoyl hydrazone (#114) are highly effective in mobilizing59Fe from 59Fe-labeled hepatocytes in vitro.28 Before starting in vivo experiments, toxicities of these compounds were tested using isolated hepatocytes in vitro.29 This model was helpful in determining nontoxic and effective concentrations of the chelators.29 

In the present study, the bile ducts of normal female rats were cannulated and the bile was collected for 2 hours before administration of the chelators (either IP or by gastric gavage); bile collection was continued for an additional 7 to 8 hours after drug administration. Each experimental group comprised eight animals, which before chelator administration, served as their own controls. Before chelator treatment, biliary iron concentration was ≤ 1 μg/mL, and dramatic increases were noted within 1 hour after administration of the hydrazones (Table 1). The highest biliary iron concentration was in rats treated with pyridoxalm-fluorobenzoyl hydrazone (PFBH, #109), which increased the concentration of iron in the bile more than 100-fold within 1 hour. Rats treated with this chelator showed a peak of biliary iron excretion between 1 to 3 hours, but very high iron levels in the bile were still detectable at 8 hours after the drug administration (Table 1). The remaining compounds (#101, #107, #114, and #115) were less effective than PFBH in promoting biliary iron excretion, both in terms of increasing the biliary iron levels and the duration of their effect (Table 1). Nevertheless, all of the compounds dramatically increased the cumulative excretion of iron in the bile (Fig 2). As compared with untreated rats, which excreted about 1 μg iron in 2 hours, at 6 hours, the cumulative iron excretion was 69, 74, 122, and 194 μg after a single dose of pyridoxal 2-thiophenecarboxyl hydrazone, pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone and pyridoxalm-fluorobenzoyl hydrazone, respectively (Fig 2). PMBH and, in particular, PFBH were significantly more effective than the parent compound, PIH, which gave a 6-hour cumulative value of 59 μg Fe (Fig2). Pyridoxal 2-furoyl hydrazone was somewhat less effective, leading to the excretion of 34 μg iron in the bile in 6 hours. The efficacy of m-fluorobenzoyl hydrazone in stimulating biliary iron excretion may be related to the high lipophilicity of this compound, either as a free ligand or in a complex with iron.22 With the exception of compound #114 (pyridoxal 2-furoyl hydrazone), all acyl hydrazones tested were significantly more effective than desferrioxamine (Fig 2). Bile appears to be the primary route of iron excretion after the administration of these compounds, as none of the hydrazones tested significantly increased urinary iron excretion (Table 2).

Table 1.

Concentration of Iron in Bile (μg/mL) After IP Administration of the Chelators

Chelator Time (h) PBH (101) PMBH (107) PFBH (109)PFH (114) PTCH (115) DFO
−2  0.39 ± 0.14 0.79 ± 0.21  0.49 ± 0.10  1.06 ± 0.38 0.37 ± 0.1  0.66 ± 0.18  
−1  0.35 ± 0.08 0.76 ± 0.21  0.70 ± 0.10  0.89 ± 0.38 0.67 ± 0.27  0.71 ± 0.13  
+1  30.10 ± 5.70 36.1 ± 13.8  88.50 ± 25.80  28.77 ± 8.48 39.50 ± 7.40  21.23 ± 2.34  
+2  39.30 ± 9.10 64.20 ± 10.30  46.90 ± 20.20  15.30 ± 2.84 81.30 ± 29.40  12.48 ± 7.52  
+3  32.00 ± 6.70 62.40 ± 7.50  85.60 ± 33.30  7.91 ± 3.29 58.80 ± 20.70  4.78 ± 4.53  
+4  20.10 ± 6.50 55.10 ± 9.30  1.60 ± 23.80  5.05 ± 2.89 34.80 ± 12.90  1.05 ± 0.48  
+5  10.60 ± 3.80 30.50 ± 8.10  86.60 ± 31.40  3.45 ± 2.05 26.70 ± 10.20  0.94 ± 0.59  
+6  3.60 ± 1.90 19.70 ± 5.30  25.20 ± 13.50  2.30 ± 1.49 13.80 ± 6.50  0.93 ± 0.50  
+7  1.80 ± 0.70 8.20 ± 3.30  19.80 ± 2.60  1.81 ± 0.64 2.80 ± 1.40  —  
8  0.67 ± 0.22 3.20 ± 1.1   1.27 ± 0.53  1.60 ± 0.70 — 
Chelator Time (h) PBH (101) PMBH (107) PFBH (109)PFH (114) PTCH (115) DFO
−2  0.39 ± 0.14 0.79 ± 0.21  0.49 ± 0.10  1.06 ± 0.38 0.37 ± 0.1  0.66 ± 0.18  
−1  0.35 ± 0.08 0.76 ± 0.21  0.70 ± 0.10  0.89 ± 0.38 0.67 ± 0.27  0.71 ± 0.13  
+1  30.10 ± 5.70 36.1 ± 13.8  88.50 ± 25.80  28.77 ± 8.48 39.50 ± 7.40  21.23 ± 2.34  
+2  39.30 ± 9.10 64.20 ± 10.30  46.90 ± 20.20  15.30 ± 2.84 81.30 ± 29.40  12.48 ± 7.52  
+3  32.00 ± 6.70 62.40 ± 7.50  85.60 ± 33.30  7.91 ± 3.29 58.80 ± 20.70  4.78 ± 4.53  
+4  20.10 ± 6.50 55.10 ± 9.30  1.60 ± 23.80  5.05 ± 2.89 34.80 ± 12.90  1.05 ± 0.48  
+5  10.60 ± 3.80 30.50 ± 8.10  86.60 ± 31.40  3.45 ± 2.05 26.70 ± 10.20  0.94 ± 0.59  
+6  3.60 ± 1.90 19.70 ± 5.30  25.20 ± 13.50  2.30 ± 1.49 13.80 ± 6.50  0.93 ± 0.50  
+7  1.80 ± 0.70 8.20 ± 3.30  19.80 ± 2.60  1.81 ± 0.64 2.80 ± 1.40  —  
8  0.67 ± 0.22 3.20 ± 1.1   1.27 ± 0.53  1.60 ± 0.70 — 
Fig. 2.

Cumulative excretion of iron in the bile of rats injected IP with pyridoxal-derived hydrazones. The bile ducts of normal rats were cannulated and the bile was collected for 2 hours, after which the hydrazones were injected IP (0.2 mmol/kg body weight) and then bile collection continued as indicated.

Fig. 2.

Cumulative excretion of iron in the bile of rats injected IP with pyridoxal-derived hydrazones. The bile ducts of normal rats were cannulated and the bile was collected for 2 hours, after which the hydrazones were injected IP (0.2 mmol/kg body weight) and then bile collection continued as indicated.

Close modal
Table 2.

Urinary Excretion of Fe After IP Administration of the Chelators

Chelator No. Fe (μg/18 h)
Control  29.88 ± 9.42  
PBH  101  25.26 ± 3.79  
PMHB 107  65.40 ± 29.89  
PFBH  109  46.40 ± 10.33 
PFH  114  30.23 ± 10.91  
PTCH  115 44.90 ± 15.34  
DFO   30.04 ± 14.31 
Chelator No. Fe (μg/18 h)
Control  29.88 ± 9.42  
PBH  101  25.26 ± 3.79  
PMHB 107  65.40 ± 29.89  
PFBH  109  46.40 ± 10.33 
PFH  114  30.23 ± 10.91  
PTCH  115 44.90 ± 15.34  
DFO   30.04 ± 14.31 

Three of the most efficient hydrazones (PFBH, PMBH, and PTCH) were further tested after administration by gastric gavage. The hydrazones were less effective in increasing biliary iron excretion when administered by gavage (Table 3) compared with IP administration (see Table 1). The most effective chelator after gastric administration was pyridoxal p-methoxybenzoyl hydrazone (PMBH) which, within 1 hour, increased biliary iron concentration more than 10-fold and maintained a high iron content in the bile for the additional 5 hours (Table 3). Consequently, PMBH given intragastrically significantly increased cumulative excretion of iron, resulting in a 6-hour cumulative value of 34 μg Fe (Fig3). As compared with PFBH, PMBH is more hydrophilic,28 a property that would seem to make this compound more soluble than PFBH in gastrointestinal fluids. If so, the availability of PMBH for absorption would be higher than that of PFBH, and this could explain the higher efficacy of PMBH, as compared with PFBH, when this compound was administered by gavage. Gastric administration of PMBH, PFBH, and PTCH did not increase urinary iron excretion (Table 4).

Table 3.

Concentration of Iron in Bile (μg/mL) After Administration of the Chelators by Gastric Gavage

Chelator Time (h) PMBH (107) PFBH (109)PTCH (115)
−2  1.01 ± 0.08  0.61 ± 0.14 0.23 ± 0.07  
+1  11.26 ± 6.06  6.72 ± 4.11 3.94 ± 2.56  
+2  6.38 ± 1.94  1.20 ± 0.19 3.96 ± 2.22  
+3  4.61 ± 2.86  0.85 ± 0.26 3.52 ± 2.22  
+4  7.55 ± 4.98  0.92 ± 0.15 4.17 ± 4.24  
+5  5.90 ± 2.82  0.82 ± 0.28 3.16 ± 2.82  
+6  6.98 ± 3.39  0.73 ± 0.28 2.37 ± 2.05 
Chelator Time (h) PMBH (107) PFBH (109)PTCH (115)
−2  1.01 ± 0.08  0.61 ± 0.14 0.23 ± 0.07  
+1  11.26 ± 6.06  6.72 ± 4.11 3.94 ± 2.56  
+2  6.38 ± 1.94  1.20 ± 0.19 3.96 ± 2.22  
+3  4.61 ± 2.86  0.85 ± 0.26 3.52 ± 2.22  
+4  7.55 ± 4.98  0.92 ± 0.15 4.17 ± 4.24  
+5  5.90 ± 2.82  0.82 ± 0.28 3.16 ± 2.82  
+6  6.98 ± 3.39  0.73 ± 0.28 2.37 ± 2.05 
Fig. 3.

Cumulative excretion of iron in bile of rats after gastric administration of pyridoxal-derived hydrazones. The bile ducts of normal rats were cannulated and the bile was collected for 2 hours, after which the hydrazones were administered by gavage (0.2 mmol/kg body weight) and then bile collection continued as indicated.

Fig. 3.

Cumulative excretion of iron in bile of rats after gastric administration of pyridoxal-derived hydrazones. The bile ducts of normal rats were cannulated and the bile was collected for 2 hours, after which the hydrazones were administered by gavage (0.2 mmol/kg body weight) and then bile collection continued as indicated.

Close modal
Table 4.

Urinary Excretion of Iron After Administration of the Chelators by Gastric Gavage

Chelator No. Fe (μg/18 h)
Control  12.50 ± 7.20  
PMBH  107  9.65 ± 3.51  
PFBH 109  8.80 ± 4.13  
PTCH  115 14.80 ± 3.72 
Chelator No. Fe (μg/18 h)
Control  12.50 ± 7.20  
PMBH  107  9.65 ± 3.51  
PFBH 109  8.80 ± 4.13  
PTCH  115 14.80 ± 3.72 

These results, as well as our previous observations,16suggest that the limited oral efficacy of PIH and other acyl hydrazones is caused by lower absorption. Similarly, Brittenham's27evaluation of PIH in patients has yielded lower than expected effect on iron excretion at doses permissible for clinical use. Because PIH was given as a powder in gelatin capsules, it appears likely that the chelator was poorly available for absorption. Hence, a more bioavailable formulation of PIH and its analogs should be designed and evaluated as a means of increasing Fe excretion. One promising strategy may involve the use of chelators encapsulated into biodegradable polymers.33 However, the bioavailability of PIH and analogs may also be limited by hydrolysis of acyl hydrazones in the stomach, as it has been reported that these compounds hydrolyze in strongly acidic solutions.34 

A clinically useful iron chelator should have high affinity for iron, but low affinity for all other biologically important cations. It is well known that DFO fullfils this criterion. Importantly, PIH and several of its analogs have very low affinity for Ca(II) and Mg(II) and complexation with these ions only occurs at pH greater than 8.35 Hence, chelation of these biologically important cations should not occur under physiologic conditions. Although the PIH class of chelators can bind Zn(II) at pH 7.4, their affinity for Zn(II) is much less than for Fe(III),35 and complexation of Zn(II) probably does not occur in vivo. In rats, PIH did not increase biliary excretion of zinc and copper.16 

One of the aims of this study was to identify a chelator with the highest efficacy to promote biliary iron excretion at a relatively low dose (0.2 mmol/kg). It is possible that at this dose the chelators do not produce maximum effects, and further experiments are being planned to examine whether PMBH and PFBH would be more effective at higher doses administered either IP or orally. DFO is known to promote urinary iron excretion in iron overloaded rats,36 and it should be pointed out that in this study we used rats that were not iron overloaded. The use of noniron overloaded rats can probably explain low urinary iron excretion after DFO administration.

In conclusion, this study showed that pyridoxal hydrazones with benzoyl (#101), p-methoxybenzoyl (#107), m-fluorobenzoyl (#109), and 2-thiophene-carboxyl (#115) substituents show potential as candidate iron chelating drugs. The most promising compounds are pyridoxal m-fluorobenzoyl hydrazone (#109) and pyridoxalp-methoxybenzoyl hydrazone (#107) that deserve further vigorous evaluation for iron chelation therapy.

The excellent technical assistance of Jana Tumova and Eva Nagy is gratefully acknowledged. We would like to thank Sandy Fraiberg for her excellent editorial assistance.

Supported by a grant from the Medical Research Council of Canada, Ottawa, Cananda; and Grant No. 0259-3 from the Czech Ministry of Health, Prague, Czech Republic.

Presented at the 37th Annual American Society of Hematology Meeting, Seattle, WA, December 1-5, 1995 and published in abstract form (Blood 86:300a, 1995 [suppl 1]).

Address reprint requests to Premysl Ponka, MD, PhD, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Cote Ste-Catherine Rd, Montreal, Quebec, Canada H3T 1E2.

The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" is accordance with 18 U.S.C. section 1734 solely to indicate this fact.

1
Porter J, Huehns E, Hider R: The development of iron chelating drugs. Ballière's Clin Haematol 2:257, 1989
2
Hershko
C
Iron chelators
Brock
JH
Halliday
JW
Pippard
MJ
Powell
LW
Iron Metabolism in Health and Disease.
1994
391
Saunders
Philadelphia, PA
3
Hoffbrand
AV
Prospects for oral chelation therapy.
J Lab Clin Med
123
1994
492
4
Kontoghiorges
GJ
Aldouri
MA
Hoffbrand
AV
Effective chelation of iron in β-thalassemia with the oral chelator 1,2-dimethyl-3-hydroxypyrid-4-one.
BMJ
295
1987
1509
5
Olivieri
NF
Koren
G
St Louis
P
Freedman
MH
McClelland
RA
Templeton
DM
Studies of the oral chelators 1,2-dimethyl-3-hydroxypyrid-4-one in thalassemia patients.
Semin Hematol
27
1990
101
6
Hoffbrand
AV
Barlett
AN
Veys
PA
O'Connor
NT
Kontoghiorghes
GJ
Agranulocytosis and thrombocytopenia in patients with Blackfan-Diamond Anaemia during oral chelator trial.
Lancet
2
1989
457
7
Cunningham
JM
Al-Refaie
FN
Hunter
AE
Sheppard
LN
Hoffbrand
AV
Differential toxicity of α-keto hydroxypyridine iron chelators and desferrioxamine to human haemopoietic precursors in vitro.
Eur J Haematol
52
1994
176
8
Al-Refaie
FN
Wonke
B
Hoffbrand
AV
Deferiprone-associated myelotoxicity.
Eur J Haematol
53
1994
298
9
Al-Refaie FN, Hoffbrand AV: Oral iron-chelating therapy: The L1 experience. Ballière's Clin Haematol 7:941, 1994
10
Hoffbrand
AV
Oral iron chelation.
Semin Hematol
33
1996
1
11
Olivieri
NF
Brittenham
GM
Iron chelation therapy and treatment of thalassemia.
Blood
89
1997
739
12
Hoffbrand
AV
Al-Refaie
F
Davis
B
Siritanakatkul
N
Jackson
BFA
Cochrane
J
Prescott
E
Wonke
B
Long-term trial of deferriprone in 51 transfusion-dependent iron overloaded patients.
Blood
91
1998
295
13
(suppl 1)
Olivieri
NF
Brittenham
GM
Final results of the randomized trial of deferiprone (L1) and deferoxamine (DFO).
Blood
90
1997
264a
14
Ponka
P
Borova
J
Neuwirt
J
Fuchs
O
Mobilization of iron from reticulocytes.
FEBS Lett
97
1979
317
15
Ponka
P
Borova
J
Neuwirt
J
Fuchs
O
Necas
E
A study of intracellular iron metabolism using pyridoxal isonicotinoyl hydrazone and other synthetic chelating agents.
Biochim Biophys Acta
586
1979
278
16
Cikrt
M
Ponka
P
Necas
E
Neuwirt
J
Biliary iron excretion in rats following pyridoxal isonicotinoyl hydrazone.
Br J Haematol
45
1980
275
17
Hoy
T
Humphreys
J
Jacobs
A
Williams
A
Ponka
P
Effective iron chelation following oral administration of an isoniazid-pyridoxal hydrazone.
Br J Haematol
43
1979
443
18
Hershko
C
Avramovici-Grisaru
S
Link
G
Gelfand
L
Sarel
S
Mechanisms of in vivo chelation by pyridoxal isonicotinoyl hydrazone and other imino derivatives of pyridoxal.
J Lab Clin Med
98
1991
99
19
Johnson
DR
Pippard
MJ
Murphy
TB
Rose
NJ
An in vivo evaluation of iron-chelating drugs derived from pyridoxal and its analogues.
J Pharmacol Exp Ther
221
1982
399
20
Williams
A
Hoy
T
Pugh
A
Jacobs
A
Pyridoxal complexes as potential chelating agents for oral therapy in transfusional iron overload.
J Pharm Pharmacol
34
1982
730
21
Ponka
P
Grady
RW
Wilczynska
A
Schulman
HM
The effect of various chelating agents on the mobilization of iron from reticulocytes in the presence and absence of pyridoxal isonicotinoyl hydrazone.
Biochim Biophys Acta
802
1984
477
22
Baker
E
Vitolo
ML
Webb
JM
Iron chelation by pyridoxal isonicotinoyl hydrazone and analogues in hepatocytes in culture.
Biochem Pharmacol
34
1985
3011
23
Vitolo
ML
Pyridoxal isonicotinoyl hydrazone (PIH), a promising new iron chelator
Fucharoen
S
Rowley
PT
Paul
NW
Thalassemia: Pathophysiology and Management Part B, March of Dimes Birth Defects Foundation, Birth Defects Original Article Series (vol 23, number 5B).
1987
63
Liss
New York, NY
24
Ponka
P
Richardson
D
Baker
E
Schulman
HM
Edward
JT
Effect of pyridoxal isonicotinoyl hydrazone and other hydrazones on iron release from macrophages, reticulocytes and hepatocytes.
Biochem Biophys Acta
967
1988
122
25
Sharma
BK
Tavill
AS
Louis
LM
Varnes
AW
Predominance of biliary iron chelates in iron-loaded rats in vivo during I.V. deferoxamine (DF) or pyridoxal isonicotinoyl hydrazone (PIH).
Hepatology
8
1988
1240
26
Sharma
BK
Tavill
AS
Louis
LN
Wiessen
E
Varnes
AW
Enteral pyridoxal isonicotinoyl hydrazone (PIH) is an effective chelator in experimental iron overload by promotion of biliary iron excretion.
Hepatology
10
1989
573
27
Brittenham
GM
Pyridoxal isonicotinoyl hydrazone: An effective iron-chelator after oral administration.
Semin Hematol
27
1990
112
28
Baker
E
Richardson
DR
Gross
S
Ponka
P
Evaluation of the iron chelation potential of pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde using the hepatocyte in culture.
Hepatology
15
1992
492
29
Nerudova J, Blaha K, Jehlickova H, Cikrt M: Testing of acyl hydrazones in mobilization of iron. Proceedings of the Seventeenth Symposium on Xenobiochemistry, May 30-31, 1991, Abstract No 6, Hradec Kralove, Czech Republic
30
Edward
JT
Gauthier
M
Chubb
FL
Ponka
P
Synthesis of new acylhydrazones as iron-chelating compounds.
J Chem Eng Data
33
1988
538
31
Cikrt
M
Biliary excretion of 203Hg, 64Cu, 52Mn and 210Pb in the rat.
Br J Ind Med
29
1972
74
32
(suppl 1)
Östlund
K
Studies on the metabolism of methyl mercury and dimethylmercury in mice.
Acta Pharmacol Toxicol
27
1969
31
33
Golenser
J
Domb
A
Teomin
D
Tsafack
A
Nisim
O
Ponka
P
Cabantchik
ZI
The treatment of animal models of malaria with iron chelators by use of novel polymeric device for slow drug release.
J Pharmacol Exp Ther
281
1997
1127
34
Richardson
D
Vitolo
LW
Baker
E
Webb
J
Pyridoxal isonicotinoyl hydrazone and analogues. Study of their stability in acid, neutral and basic aqueous solutions by ultraviolet-visible spectrophotometry.
Biol Met
2
1989
69
35
Richardson
DR
Hefter
GT
May
PM
Webb
J
Baker
E
Iron chelators of the pyridoxal isonicotinoyl hydrazone class III. Formation constants with calcium(II), magnesium(II) and zinc(II).
Biol Met
2
1989
161
36
Hershko
C
Grady
RW
Cerami
A
Mechanism of iron chelation in the hypertransfused rat: Definition of the two alternative pathways of iron mobilization.
J Lab Clin Med
92
1978
144
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