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Strategies to rescue the consequences of inducible arginase-1 deficiency in mice.

Ballantyne LL, Sin YY, St Amand T, Si J, Goossens S, Haenebalcke L, Haigh JJ, Kyriakopoulou L, Schulze A, Funk CD - PLoS ONE (2015)

Bottom Line: Arginase-1 catalyzes the conversion of arginine to ornithine and urea, which is the final step of the urea cycle used to remove excess ammonia from the body.Standard clinical care regimens for arginase-1 deficiency (low-protein diet, the nitrogen-scavenging drug sodium phenylbutyrate, ornithine supplementation) either failed to extend lifespan (ornithine) or only minimally prolonged lifespan (maximum 8 days with low-protein diet and drug).Delivery of an arginase-1/enhanced green fluorescent fusion construct by adeno-associated viral delivery (rh10 serotype with a strong cytomegalovirus-chicken β-actin hybrid promoter) rescued about 30% of male mice with lifespan prolongation to at least 6 months, extensive hepatic expression and restoration of significant enzyme activity in liver.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.

ABSTRACT
Arginase-1 catalyzes the conversion of arginine to ornithine and urea, which is the final step of the urea cycle used to remove excess ammonia from the body. Arginase-1 deficiency leads to hyperargininemia in mice and man with severe lethal consequences in the former and progressive neurological impairment to varying degrees in the latter. In a tamoxifen-induced arginase-1 deficient mouse model, mice succumb to the enzyme deficiency within 2 weeks after inducing the knockout and retain <2 % enzyme in the liver. Standard clinical care regimens for arginase-1 deficiency (low-protein diet, the nitrogen-scavenging drug sodium phenylbutyrate, ornithine supplementation) either failed to extend lifespan (ornithine) or only minimally prolonged lifespan (maximum 8 days with low-protein diet and drug). A conditional, tamoxifen-inducible arginase-1 transgenic mouse strain expressing the enzyme from the Rosa26 locus modestly extended lifespan of neonatal mice, but not that of 4-week old mice, when crossed to the inducible arginase-1 knockout mouse strain. Delivery of an arginase-1/enhanced green fluorescent fusion construct by adeno-associated viral delivery (rh10 serotype with a strong cytomegalovirus-chicken β-actin hybrid promoter) rescued about 30% of male mice with lifespan prolongation to at least 6 months, extensive hepatic expression and restoration of significant enzyme activity in liver. In contrast, a vector of the AAV8 serotype driven by the thyroxine-binding globulin promoter led to weaker liver expression and did not rescue arginase-1 deficient mice to any great extent. Since the induced arginase-1 deficient mouse model displays a much more severe phenotype when compared to human arginase-1 deficiency, these studies reveal that it may be feasible with gene therapy strategies to correct the various manifestations of the disorder and they provide optimism for future clinical studies.

No MeSH data available.


Related in: MedlinePlus

Ornithine supplementation does not rescue the induced arginase-1 deficiency phenotype.(A) Citrulline (Cit), ornithine (Orn), arginine (Arg) and methionine (Met) plasma concentrations are similar in control and ornithine-treated groups of 4 week old mice at baseline (n = 4). (B) Ornithine-treated mice (●, n = 4) indeed show elevations in plasma ornithine, which demonstrates the efficacy of the protocol, and have significant increases in arginine compared to control mice (■,n = 5) *, p<0.05 relative to control. (C) Mice in both groups show similar patterns of weight loss (surrogate marker of health status). Weight loss at humane endpoint was always significantly lower (*, p<0.05) than at Day +4.
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pone.0125967.g002: Ornithine supplementation does not rescue the induced arginase-1 deficiency phenotype.(A) Citrulline (Cit), ornithine (Orn), arginine (Arg) and methionine (Met) plasma concentrations are similar in control and ornithine-treated groups of 4 week old mice at baseline (n = 4). (B) Ornithine-treated mice (●, n = 4) indeed show elevations in plasma ornithine, which demonstrates the efficacy of the protocol, and have significant increases in arginine compared to control mice (■,n = 5) *, p<0.05 relative to control. (C) Mice in both groups show similar patterns of weight loss (surrogate marker of health status). Weight loss at humane endpoint was always significantly lower (*, p<0.05) than at Day +4.

Mentions: We did not previously find any evidence for alterations in plasma ornithine in mice with induced Arg1 deficiency [10], as might be expected with the loss of this enzyme and as previously observed in the juvenile lethal model [7,8]. Low ornithine levels within liver hepatocytes, however, could be present as a result of diminished arginase activity and contribute to hyperammonemia and potentially to the lethality in the inducible Arg1 knockout mouse model. Therefore, we sought to supplement ornithine levels in a representative 4-week old cohort of mice by providing it in the drinking water. At baseline, all mice were healthy and there were no differences in amino acids, citrulline and ornithine between the groups of mice (Fig 2A and data not shown; n = 4). After tamoxifen dosing, hyperargininemia was present and ornithine was significantly elevated in the ornithine-supplemented group compared to controls (Fig 2B; n = 4 or 5). There was also a small, but significant, decrease in plasma methionine in the treated group with no alterations in any other amino acids including citrulline or glutamine. Tamoxifen treatment to induce Arg1 deficiency provoked the typical time course of weight loss (Fig 2C) and phenotypic decline resulting in humane endpoints at the usual time point in both groups of mice.


Strategies to rescue the consequences of inducible arginase-1 deficiency in mice.

Ballantyne LL, Sin YY, St Amand T, Si J, Goossens S, Haenebalcke L, Haigh JJ, Kyriakopoulou L, Schulze A, Funk CD - PLoS ONE (2015)

Ornithine supplementation does not rescue the induced arginase-1 deficiency phenotype.(A) Citrulline (Cit), ornithine (Orn), arginine (Arg) and methionine (Met) plasma concentrations are similar in control and ornithine-treated groups of 4 week old mice at baseline (n = 4). (B) Ornithine-treated mice (●, n = 4) indeed show elevations in plasma ornithine, which demonstrates the efficacy of the protocol, and have significant increases in arginine compared to control mice (■,n = 5) *, p<0.05 relative to control. (C) Mice in both groups show similar patterns of weight loss (surrogate marker of health status). Weight loss at humane endpoint was always significantly lower (*, p<0.05) than at Day +4.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4418594&req=5

pone.0125967.g002: Ornithine supplementation does not rescue the induced arginase-1 deficiency phenotype.(A) Citrulline (Cit), ornithine (Orn), arginine (Arg) and methionine (Met) plasma concentrations are similar in control and ornithine-treated groups of 4 week old mice at baseline (n = 4). (B) Ornithine-treated mice (●, n = 4) indeed show elevations in plasma ornithine, which demonstrates the efficacy of the protocol, and have significant increases in arginine compared to control mice (■,n = 5) *, p<0.05 relative to control. (C) Mice in both groups show similar patterns of weight loss (surrogate marker of health status). Weight loss at humane endpoint was always significantly lower (*, p<0.05) than at Day +4.
Mentions: We did not previously find any evidence for alterations in plasma ornithine in mice with induced Arg1 deficiency [10], as might be expected with the loss of this enzyme and as previously observed in the juvenile lethal model [7,8]. Low ornithine levels within liver hepatocytes, however, could be present as a result of diminished arginase activity and contribute to hyperammonemia and potentially to the lethality in the inducible Arg1 knockout mouse model. Therefore, we sought to supplement ornithine levels in a representative 4-week old cohort of mice by providing it in the drinking water. At baseline, all mice were healthy and there were no differences in amino acids, citrulline and ornithine between the groups of mice (Fig 2A and data not shown; n = 4). After tamoxifen dosing, hyperargininemia was present and ornithine was significantly elevated in the ornithine-supplemented group compared to controls (Fig 2B; n = 4 or 5). There was also a small, but significant, decrease in plasma methionine in the treated group with no alterations in any other amino acids including citrulline or glutamine. Tamoxifen treatment to induce Arg1 deficiency provoked the typical time course of weight loss (Fig 2C) and phenotypic decline resulting in humane endpoints at the usual time point in both groups of mice.

Bottom Line: Arginase-1 catalyzes the conversion of arginine to ornithine and urea, which is the final step of the urea cycle used to remove excess ammonia from the body.Standard clinical care regimens for arginase-1 deficiency (low-protein diet, the nitrogen-scavenging drug sodium phenylbutyrate, ornithine supplementation) either failed to extend lifespan (ornithine) or only minimally prolonged lifespan (maximum 8 days with low-protein diet and drug).Delivery of an arginase-1/enhanced green fluorescent fusion construct by adeno-associated viral delivery (rh10 serotype with a strong cytomegalovirus-chicken β-actin hybrid promoter) rescued about 30% of male mice with lifespan prolongation to at least 6 months, extensive hepatic expression and restoration of significant enzyme activity in liver.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.

ABSTRACT
Arginase-1 catalyzes the conversion of arginine to ornithine and urea, which is the final step of the urea cycle used to remove excess ammonia from the body. Arginase-1 deficiency leads to hyperargininemia in mice and man with severe lethal consequences in the former and progressive neurological impairment to varying degrees in the latter. In a tamoxifen-induced arginase-1 deficient mouse model, mice succumb to the enzyme deficiency within 2 weeks after inducing the knockout and retain <2 % enzyme in the liver. Standard clinical care regimens for arginase-1 deficiency (low-protein diet, the nitrogen-scavenging drug sodium phenylbutyrate, ornithine supplementation) either failed to extend lifespan (ornithine) or only minimally prolonged lifespan (maximum 8 days with low-protein diet and drug). A conditional, tamoxifen-inducible arginase-1 transgenic mouse strain expressing the enzyme from the Rosa26 locus modestly extended lifespan of neonatal mice, but not that of 4-week old mice, when crossed to the inducible arginase-1 knockout mouse strain. Delivery of an arginase-1/enhanced green fluorescent fusion construct by adeno-associated viral delivery (rh10 serotype with a strong cytomegalovirus-chicken β-actin hybrid promoter) rescued about 30% of male mice with lifespan prolongation to at least 6 months, extensive hepatic expression and restoration of significant enzyme activity in liver. In contrast, a vector of the AAV8 serotype driven by the thyroxine-binding globulin promoter led to weaker liver expression and did not rescue arginase-1 deficient mice to any great extent. Since the induced arginase-1 deficient mouse model displays a much more severe phenotype when compared to human arginase-1 deficiency, these studies reveal that it may be feasible with gene therapy strategies to correct the various manifestations of the disorder and they provide optimism for future clinical studies.

No MeSH data available.


Related in: MedlinePlus