Development and characterization of an animal model of carnitine deficiency.
Mammals cover their carnitine needs by diet and biosynthesis. The last step of carnitine biosynthesis is the conversion of butyrobetaine to carnitine by butyrobetaine hydroxylase. We investigated the effect of N-trimethyl-hydrazine-3-propionate (THP), a butyrobetaine analogue, on butyrobetaine hydroxylase kinetics, and carnitine biosynthesis and body homeostasis in rats fed a casein-based or a vegetarian diet. The K(m )of butyrobetaine hydroxylase purified from rat liver was 41 +/- 9 micromol x L(-1) for butyrobetaine and 37 +/- 5 micromol x L(-1) for THP, and THP was a competitive inhibitor of butyrobetaine hydroxylase (K(i) 16 +/- 2 micromol x L(-1)). In rats fed a vegetarian diet, renal excretion of total carnitine was increased by THP (20 mg.100 g(-1) x day(-1) for three weeks), averaging 96 +/- 36 and 5.3 +/- 1.2 micromol x day(-1) in THP-treated and control rats, respectively. After three weeks of treatment, the total carnitine plasma concentration (8.8 +/- 2.1 versus 52.8 +/- 11.4 micromol x L(-1)) and tissue levels were decreased in THP-treated rats (liver 0.19 +/- 0.03 versus 0.59 +/- 0.08 and muscle 0.24 +/- 0.04 versus 1.07 +/- 0.13 micromol x g(-1)). Carnitine biosynthesis was blocked in THP-treated rats (-0.22 +/- 0.13 versus 0.57 +/- 0.21 micromol x 100 g(-1) x day(-1)). Similar results were obtained in rats treated with the casein-based diet. THP inhibited carnitine transport by rat renal brush-border membrane vesicles competitively (K(i) 41 +/- 3 micromol x L(-1)). Palmitate metabolism in vivo was impaired in THP-treated rats and the livers showed mixed steatosis. Steady-state mRNA levels of the carnitine transporter rat OCTN2 were increased in THP-treated rats in skeletal muscle and small intestine. In conclusion, THP inhibits butyrobetaine hydroxylase competitively, blocks carnitine biosynthesis in vivo and interacts competitively with renal carnitine reabsorption. THP-treated rats develop systemic carnitine deficiency over three weeks and can therefore serve as an animal model for human carnitine deficiency.
Department of Clinical Pharmacology and Toxicology, University of Basel, Switzerland.
M
M
Spaniol
H
H
Brooks
L
L
Auer
A
A
Zimmermann
M
M
Solioz
B
B
Stieger
S
S
Krähenbühl
D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002331:Carnitine / Q000097:blood / Q000172:deficiency* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics; D017931:DNA Primers; D004195:Disease Models, Animal; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D008763:Methylhydrazines / Q000008:administration & dosage; D008871:Microvilli / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D000074058:Solute Carrier Family 22 Member 5; D015854:Up-Regulation; D050563:gamma-Butyrobetaine Dioxygenase
D002352:Carrier Proteins; D017931:DNA Primers; D008565:Membrane Proteins; D008763:Methylhydrazines; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; C050147:3-(2,2,2-trimethylhydrazine)propionate; D006899:Mixed Function Oxygenases; D050563:gamma-Butyrobetaine Dioxygenase; D002331:Carnitine