Ingalill Nordin

CARNITINE DEFICIENCY INDUCED BY PIVAMPICILLIN AND PIVMECILLINAM THERAPY

Short-term administration of pivampicillin and pivmecillinam resulted in a reduction of serum carnitine concentration and an increase in excretion of acylcarnitine in urine. These changes persisted for more than ten days after cessation of therapy. In seven girls on long-term treatment with a mixture of pivampicillin and pivmecillinam the mean total serum carnitine concentration fell to 15% (7-27%) of pretreatment values. The acylcarnitine fraction was 11-57% of total carnitine, compared with less than 2% before treatment. Muscle carnitine concentrations in two girls treated with the antibiotics for 22 and 30 months were only 10% of the mean reference value. These concentrations in serum and muscle are in the range encountered in patients with carnitine deficiencies of other aetiologies in which life-threatening metabolic crises may arise. The risk of adverse effects from prodrugs that give rise to pivalic acid should be seriously considered, particularly in patients under metabolic stress.

Effects of pivalic acid-containing prodrugs on carnitine homeostasis and on response to fasting in children.

Treatment of 17 children aged 2-9.5 years with a combination of pivmecillinam and pivampicillin (250-500 mumol 24 h-1) for more than 1 year resulted in a reduction of the free carnitine concentration in serum and muscle to less than 10% of the mean reference value. The decline in serum was slow, with an estimated half-life of about 5 months. Spontaneous replenishment occurred at about the same slow rate. Thus, there is no increase in endogenous carnitine synthesis as a response to increased demand of carnitine for detoxification. Supplementation with carnitine during treatment required at least a four-fold molar excess over pivalic acid to achieve and sustain a normal carnitine concentration. The replenishment of carnitine occurred with a half-life of 1.1-3.0 months. From determination of muscle-carnitine concentration in patients treated with pivaloyl-containing antibiotics and in patients with organic aciduris, we conclude that serum carnitine is a good predictor of carnitine stores in the body. Six non-supplemented patients with a serum free-carnitine concentration of 0.7-2.6 mumol l-1 had an inadequate ketone-body increase during a 24-h fast. Vomiting, nausea and tiredness occurred in three cases following the fasting period. After normalization of the serum-carnitine concentration, a normal response to fasting was observed. Thus, in some organic acidurias, for example medium-chain acyl-CoA dehydrogenase deficiency, a low liver concentration of carnitine may be an important contributing factor to hypoglycaemic and Reye-like attacks. We believe that prodrugs which contain pivalic acid should be avoided if acceptable alternatives exist. If used, supplementation with at least four-fold molar excess of carnitine is advisable.

γ-Butyrobetaine hydroxylase in human kidney

The activity of γ-butyrobetaine hydroxylase [4-trimethylaminobutyrate: oxygen oxidoreductase (3-hydroxylating), EC 1.14.11.1] was determined in different parts of a human kidney removed at surgery and in five perfused human cadaver kidneys. The activity in the 100,000 g supernatant fraction of a homogenate of whole kidneys was 48 nkat·g-1 protein (range 32–70 nkat·g-1 protein). The cortex and outer medulla had four to six times higher activity than the inner medulla. A 60-fold purification from the soluble fraction of kidney homogenates with a 40% recovery was achieved by ammonium sulphate fractionation followed by DEAE-cellulose and hydroxylapatite chromatography. The enzyme had a specific activity of 2.4 μkat·g-1 protein but was contaminated to a minor degree by other proteins as judged by polyacrylamide gel electrophoresis. The Km values for γ-butyrobetaine, 2-oxoglutarate and oxygen were 0.2 mmol/1, 0.3 mmol/1 and 5.5% (by volume in the gas phase). There was an absolute requirement for ferrous ion. Ha...

Uncoupling in the γ-butyrobetaine hydroxylase reaction by D=- and L=-carnitine

Abstract In the presence of D = -carnitine significant decarboxylation of 2-oxoglutarate occurs with γ-butyrobetaine hydroxylase (EC 1.14.11.1) both from Pseudomonas sp AK 1 and from human kidney. No product was formed from carnitine when D = L = -carnitine was incubated with either enzyme but succinate was formed in 1:1 stoichiometry to decarboxylation using D = -carnitine and the human enzyme. L = -Carnitine is also an uncoupler for the human enzyme. There is no significant decarboxylation of 2-oxoglutarate in the absence of a substrate, but during normal catalysis in the presence of γ-butyrobetaine the formation of CO2 from 2-oxoglutarate exceeds carnitine formation with 20% for the human enzyme.

Uncoupling and isotope effects in γ-butyrobetaine hydroxylation

Replacement of unlabeled γ-butyrobetaine with γ-[2,3,4-2H6]butyrobetaine has a profound effect on the stoichiometry between decarboxylation of 2-oxoglutarate and hydroxylation in the reaction catalyzed by human γ -butyrobetaine hydroxylase. The ratios between decarboxylation and hydroxylation are 1.16 with Unlabeled and 7.48 with deuterated γ-butyrobetaine as substrate. From these ratios an internal isotope effect of 41 has been calculated. DV in the overall reaction measured as 2- oxoglutarate decarboxylation is 2.5 and DV/K is 1.0. For γ-butyrobetaine hydroxylase fromPseudomonas sp. AK 1, 2-oxoglutarate decarboxylation exceeds hydroxylation with 10% when deuterated γ-butyrobetaine is used. No excess was found with unlabeled substrate and no internal isotope effect could be calculated. DV for the bacterial enzyme is 6.