Levels in neurotransmitter precursor amino acids correlate with mental health in patients with breast cancer

Breast cancer is the most common cancer among females. Approximately 30% of cancer patients develop depression or depressive adaptation disorder within 5 years post diagnosis. Low grade inflammation and subsequent changes in neurotransmitter levels could be the pathophysiological link. In the current study we investigated the association of neurotransmitter precursor amino acids with a diagnosis of depression or state anxiety in 154 subjects suffering from breast cancer (BCA(+)), depression (DPR(+)), both or neither. Sociodemographic parameters, severity of depressive symptoms, and state anxiety (ANX) were recorded. Neopterin, kynurenine/tryptophan and phenylalanine/tyrosine were analysed by HPLC or ELISA. Significantly higher serum neopterin values were found in DPR(+) patients (p = 0.034) and in ANX(+) subjects (p = 0.008), as a marker of Th1-related inflammation. The phenylalanine/tyrosine ratio (index of the catecholamine pathway) was associated with the factors "breast cancer" and "depression" and their interaction (all p < 0.001); it was highest in the DPR(+)BCA(+) group. The kynurenine/tryptophan ratio (index of the serotonin pathway) was significantly associated with the factors "breast cancer" and "state anxiety" and their interaction (p < 0.001, p = 0.026, p = 0.02, respectively); it was highest in the ANX(+)BCA(+) group. In BCA(+) patients kynurenine/tryptophan ratios correlated with severity of state anxiety (r = 0.226, p = 0.048, uncorrected) and phenylalanine/tyrosine ratios with severity of depressive symptoms (r = 0.376, p < 0.05, corrected). In conclusion, levels of neurotransmitter precursor amino acids correlate with mental health, an effect which was much more pronounced in BCA(+) patients than in BCA(-) subjects. Aside from identifying underlying pathophysiological mechanisms, these results could be the basis for future treatment studies: in BCA(+) patients with depression the use of serotonin-noradrenaline reuptake inhibitors might be recommended while in those with predominant anxiety selective serotonin reuptake inhibitors might be the treatment of choice.

[Difference and distance between the central and thinnest points of the cornea: impact of refractive state, age and ocular side]

BACKGROUND

The aim of the study was to quantify the difference in corneal thickness between the central and thinnest points (∆PachyZ-PachyD), the distance between the center of the cornea and its thinnest point (vector length PachyD) and to explore the impact of refractive state, age and ocular side.

PATIENTS AND METHODS

This was a multicenter, retrospective, cross-sectional study and medical records of 16,872 eyes were reviewed. The Orbscan® (Bausch and Lomb) procedure was used for pachymetry and keratometry.

RESULTS

The results showed that ∆PachyZ-PachyD and vector length PachyD were higher in hyperopic eyes (∆PachyZ-PachyD: 11.99 ± 12.08 µm, vector length PachyD: 0.85 ± 0.44 mm) compared to myopic eyes (∆PachyZ-PachyD: 9.2 ± 7.86 µm, vector length PachyD: 0.7 ± 0.37 mm; p < 0.001). Refractive state, age and ocular side demonstrated an independent, statistically significant impact on ∆PachyZ-PachyD and vector length PachyD.

CONCLUSIONS

As a result of the significant impact of refractive state, age and ocular side on ∆PachyZ-PachyD and vector length PachyD, these variables should be considered in a normative data collection.

In vivo and in vitro investigations of heterozygous nebulin knock-out mice disclose a mild skeletal muscle phenotype

Nemaline myopathy is the most common congenital skeletal muscle disease, and mutations in the nebulin gene account for 50% of all cases. Recent studies suggest that the disease severity might be related to the nebulin expression levels. Considering that mutations in the nebulin gene are typically recessive, one would expect that a single functional nebulin allele would maintain nebulin protein expression which would result in preserved skeletal muscle function. We investigated skeletal muscle function of heterozygous nebulin knock-out (i.e., nebulin(+/-)) mice using a multidisciplinary approach including protein and gene expression analysis and combined in vivo and in vitro force measurements. Skeletal muscle anatomy and energy metabolism were studied strictly non-invasively using magnetic resonance imaging and 31P-magnetic resonance spectroscopy. Maximal force production was reduced by around 16% in isolated muscle of nebulin(+/-) mice while in vivo force generating capacity was preserved. Muscle weakness was associated with a shift toward a slower proteomic phenotype, but was not related to nebulin protein deficiency or to an impaired energy metabolism. Further studies would be warranted in order to determine the mechanisms leading to a mild skeletal muscle phenotype resulting from the expression of a single nebulin allele.

S-15261, a new anti-hyperglycemic agent, reduces hepatic glucose production through direct and insulin-sensitizing effects

S-15261 is a new oral anti-hyperglycemic agent that increases insulin sensitivity in various insulin-resistant animal models. The aim of this study was to determine the short- and long-term effects of S-15261 and its metabolites (S-15511 and Y-415) on fatty acid and glucose metabolism in hepatocytes isolated from 24-h starved rats. During short-term exposure (1h) neither S-15261 nor its metabolites affected fatty acid oxidation whatever the concentration used. By contrast, S-15261 and its two metabolites reduced the rates of glucose production from lactate/pyruvate and dihydroxyacetone. Using crossover plot analysis, it was shown that Y-415 reduced hepatic gluconeogenesis upstream the formation of dihydroxyacetone phosphate. After 48 h in culture, S-15261 and its two metabolites reduced the rates of glucose production from lactate/pyruvate secondarily to a decrease in PEPCK and Glc-6-Pase mRNA levels. A part of these effects on gene expression could be due to a drug-induced reduction in PGC-1 gene expression. When hepatocytes were cultured in the presence of a submaximal concentration of insulin (10(-9)M), S-15261, through its metabolite S-15511, enhanced insulin sensitivity both on gene expression (PEPCK, Glc-6-Pase, PGC-1) and on gluconeogenesis. Furthermore, S-15261 and S-15511 induced the expression of GK and FAS genes as the result of an increased in SREBP-1c mRNA levels. Finally, S-15511 enhanced the stimulatory effect of insulin on GK mRNA level through an additional increase in SREBP-1c gene expression. In conclusion, this work reveals that S-15261 via its metabolites reduces hepatic glucose production through direct and insulin-sensitizing effects on genes encoding regulatory proteins of hepatic glucose metabolism.

Effect of metformin on fatty acid and glucose metabolism in freshly isolated hepatocytes and on specific gene expression in cultured hepatocytes

The short-term effect of metformin on fatty acid and glucose metabolism was studied in freshly incubated hepatocytes from 24-hr starved rats. Metformin (5 or 50 mM) had no effect on oleate or octanoate oxidation rates (CO(2)+ acid-soluble products), whatever the concentration used. Similarly, metformin had no effect on oleate esterification (triglycerides and phospholipid synthesis) regardless of whether the hepatocytes were isolated from starved (low esterification rates) or fed rats (high esterification rates). In contrast, metformin markedly reduced the rates of glucose production from lactate/pyruvate, alanine, dihydroxyacetone, and galactose. Using crossover plot experiments, it was shown that the main effect of metformin on hepatic gluconeogenesis was located upstream of the formation of dihydroxyacetone phosphate. Increasing the time of exposure to metformin (24 hr instead of 1 hr) led to significant changes in the expression of genes involved in glucose and fatty acid metabolism. Indeed, when hepatocytes were cultured in the presence of 50 to 500 microM metformin, the expression of genes encoding regulatory proteins of fatty acid oxidation (carnitine palmitoyltransferase I), ketogenesis (mitochondrial hydroxymethylgltaryl-CoA synthase), and gluconeogenesis (glucose 6-phosphatase, phosphoenolpyruvate carboxykinase) was decreased by 30 to 60%, whereas expression of genes encoding regulatory proteins involved in glycolysis (glucokinase and liver-type pyruvate kinase) was increased by 250%. In conclusion, this work suggests that metformin could reduce hepatic glucose production through short-term (metabolic) and long-term (genic) effects.

Long-chain fatty acids regulate liver carnitine palmitoyltransferase I gene (L-CPT I) expression through a peroxisome-proliferator-activated receptor alpha (PPARalpha)-independent pathway

Liver carnitine palmitoyltransferase I (L-CPT I) catalyses the transfer of long-chain fatty acid (LCFA) for translocation across the mitochondrial membrane. Expression of the L-CPT I gene is induced by LCFAs as well as by lipid-lowering compounds such as clofibrate. Previous studies have suggested that the peroxisome-proliferator-activated receptor alpha (PPARalpha) is a common mediator of the transcriptional effects of LCFA and clofibrate. We found that free LCFAs rather than acyl-CoA esters are the signal metabolites responsible for the stimulation of L-CPT I gene expression. Using primary culture of hepatocytes we found that LCFAs failed to stimulate L-CPT I gene expression both in wild-type and PPARalpha-null mice. These results suggest that the PPARalpha-knockout mouse does not represent a suitable model for the regulation of L-CPT I gene expression by LCFAs in the liver. Finally, we determined that clofibrate stimulates L-CPT I through a classical direct repeat 1 (DR1) motif in the promoter of the L-CPT I gene while LCFAs induce L-CPT I via elements in the first intron of the gene. Our results demonstrate that LCFAs can regulate gene expression through PPARalpha-independent pathways and suggest that the regulation of gene expression by dietary lipids is more complex than previously proposed.

Reduced hepatic fatty acid oxidation in fasting PPARalpha null mice is due to impaired mitochondrial hydroxymethylglutaryl-CoA synthase gene expression

Glucose and fatty acid metabolism (oxidation versus esterification) has been measured in hepatocytes isolated from 24 h starved peroxisome proliferator-activated receptor-alpha (PPARalpha) null and wild-type mice. In PPARalpha null mice, the development of hypoglycemia during starvation was due to a reduced capacity for hepatic gluconeogenesis secondary to a 70% lower rate of fatty acid oxidation. This was not due to inappropriate expression of the hepatic CPT I gene, which was similar in both genotypes, but to impaired mitochondrial hydroxymethylglutaryl-CoA synthase gene expression in the PPARalpha null mouse liver. We also demonstrate that hepatic steatosis of fasting PPARalpha null mice was not due to enhanced triglyceride synthesis.

Prediction of pharmacokinetic drug/drug interactions from In vitro data: interactions of the nonsteroidal anti-inflammatory drug lornoxicam with oral anticoagulants

CYP2C9 is involved in the metabolism of the oral anticoagulants warfarin, phenprocoumon, and acenocoumarol. It is also responsible for the 5'-hydroxylation of the nonsteroidal anti-inflammatory drug lornoxicam. Therefore, lornoxicam and the oral anticoagulants are potential inhibitors of their metabolism. Their inhibitory potency was investigated in microsomes from six human livers. An approach to predict pharmacokinetic interactions of lornoxicam from in vitro inhibition data was developed. Where possible, the forecasts were verified by comparison with data from clinical interaction studies. The following increases in steady-state plasma concentrations or areas under the plasma concentration-time curve of the oral anticoagulants by concomitant lornoxicam medication were predicted (values in parentheses are for healthy volunteers): (S)-warfarin, 1. 58-fold (1.32-fold for racemate); racemic-acenocoumarol, 1.28-fold (1.09-fold); (R)-acenocoumarol, 1.10-fold (1.0-fold); racemic-phenprocoumon, 1.11-fold (1.18-fold); and (S)-phenprocoumon, 1.13-fold (1.24-fold). Lornoxicam 5'-hydroxylation was competitively inhibited in vitro by both phenprocoumon (K(i) = 1.2 +/- 0.4 microM) and acenocoumarol (K(i) = 5.5 +/- 3.5 microM). The present results indicate that relatively close predictions of the interactions of lornoxicam with oral anticoagulants from in vitro data are possible under the assumption that hepatic lornoxicam concentrations are similar to its total plasma concentrations. The degree of pharmacokinetic interactions exhibited by oral anticoagulants and lornoxicam is dependent on the respective contribution of CYP2C9 to their total clearance.

Atypical expression of mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in subcutaneous adipose tissue of male rats

The mRNAs encoding mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (mtHMG-CoA synthase), the rate limiting enzyme in ketone body production, are highly expressed in subcutaneous (SC) and, to a lesser extent, in peri-epididymal (PE) rat adipose tissues. This atypical mtHMG-CoA synthase gene expression is dependent on the age (from 9 weeks of age) and sex (higher in male than in female) of the rats. In contrast, the expression of mtHMG-CoA synthase in SC adipose deposit is independent of the nutritional state (fed versus starved) or of the thermic environment (24 degrees C versus 4 degrees C). The expression of mtHMG-CoA synthase is suppressed in SC fat pads of castrated male rats whereas treatment of castrated rats with testosterone restores a normal level of expression. Moreover, testosterone injection induces the expression mtHMG-CoA synthase in SC adipose tissue of age-matched females. The presence of the mtHMG-CoA synthase immunoreactive protein confers to mitochondria isolated from SC adipose deposits, the capacity to produce ketone bodies at a rate similar to that found in liver mitochondria (SC = 13.7 +/- 0.7, liver = 16.4 +/- 1.4 nmol/min/mg prot). mtHMG-CoA synthase is expressed in the stromal vascular fraction (SVF) whatever the adipose deposit considered. While acetyl-CoA carboxylase (ACC) is only expressed in mature adipocytes, the other lipogenic enzymes, fatty acid synthase (FAS) and citrate cleavage enzyme (CCE), are expressed both in SVF cells and mature adipocytes. The expression of lipogenic enzyme genes is markedly reduced in adipocytes but not in SVF cells isolated from 48-h starved male rats. When SVF is subfractionated, mtHMG-CoA synthase mRNAs are mainly recovered in two fractions containing poorly digested structures such as microcapillaries whereas the lowest expression is found in the pre-adipocyte fraction. Interestingly, FAS and CCE mRNAs co-segregate with mtHMG-CoA synthase mRNA. The possible physiological relevance of such atypical expression of mtHMG-CoA synthase is discussed.

The N-terminal domain of rat liver carnitine palmitoyltransferase 1 mediates import into the outer mitochondrial membrane and is essential for activity and malonyl-CoA sensitivity

The rat liver carnitine palmitoyltransferase 1 (L-CPT1), an integral outer mitochondrial membrane (OMM) protein, is the key regulatory enzyme of fatty acid oxidation and is inhibited by malonyl-CoA. In vitro import of L-CPT1 into the OMM requires the presence of mitochondrial receptors and is stimulated by ATP but is membrane potential-independent. Its N-terminal domain (residues 1-150), which contains two transmembrane segments, possesses all of the information for mitochondrial targeting and OMM insertion. Deletion of this domain abrogates protein targeting, whereas its fusion to non-OMM-related proteins results in their mitochondrial targeting and OMM insertion in a manner similar to L-CPT1. Functional analysis of chimeric CPTs expressed in Saccharomyces cerevisiae shows that this domain also mediates in vivo protein insertion into the OMM. When the malonyl-CoA-insensitive CPT2 was anchored at the OMM either by a specific OMM signal anchor sequence (pOM29) or by the N-terminal domain of L-CPT1, its activity remains insensitive to malonyl-CoA inhibition. This indicates that malonyl-CoA sensitivity is an intrinsic property of L-CPT1 and that its N-terminal domain cannot confer malonyl-CoA sensitivity to CPT2. Replacement of the N-terminal domain by pOM29 results in a less folded and less active protein, which is also malonyl-CoA-insensitive. Thus, in addition to its role in mitochondrial targeting and OMM insertion, the N-terminal domain of L-CPT1 is essential to maintain an optimal conformation for both catalytic function and malonyl-CoA sensitivity.

Topological and functional analysis of the rat liver carnitine palmitoyltransferase 1 expressed in Saccharomyces cerevisiae

The rat liver carnitine palmitoyltransferase 1 (L-CPT 1) expressed in Saccharomyces cerevisiae was correctly inserted into the outer mitochondrial membrane and shared the same folded conformation as the native enzyme found in rat liver mitochondria. Comparison of the biochemical properties of the yeast-expressed L-CPT 1 with those of the native protein revealed the same detergent lability and similar sensitivity to malonyl-CoA inhibition and affinity for carnitine. Normal Michaelis-Menten kinetics towards palmitoyl-CoA were observed when careful experimental conditions were used for the CPT assay. Thus, the expression in S. cerevisiae is a valid model to study the structure-function relationships of L-CPT 1.

Denitrification of the genotoxicant 2-nitropropane: relationship to its mechanism of toxicity

1. The stabilities of the industrial chemical and constituent of cigarette smoke 2-nitropropane (2-NP) and its aci tautomer propane 2-nitronate (P2N) towards hepatic enzymes and proteins such as serum proteins and oxyhaemoglobin were investigated in vitro in biological (hepatocytes and subcellular liver fractions) and model systems (serum proteins, oxyhaemoglobin, methylene blue). 2. Denitrification of 2-NP, P2N and 2-deutero 2-nitropropane (2H-NP) occurred in murine hepatocytes significantly faster than in rat cells. For 2-NP the rates were 1271 +/- 167 versus 820 +/- 125 pmol nitrite x min-1 x 10(6) cells-1. 3. A similar observation was made in microsomes, where 2-NP denitrification was 1460 +/- 110 (mouse) versus 480 +/- 80 pmol nitrite x min-1 x mg protein-1 (rat). 4. The major NO2(-)-forming activity was found to be localized in the microsomal fraction. 5. Conversion of 2-NP into P2N, either chemically or enzymatically, was a prerequisite for rapid denitrification. 6. Serum proteins and oxyhaemoglobin proved to be capable of denitrifying P2N (198 +/- 24 pmol nitrite x min-1 x mg protein-1 and 7.1 +/- 1.0 nmol nitrite x min-1 x nmol HbO2(-1) respectively), but were much less active towards 2-NP (24 +/- 2 pmol nitrite x min-1 x mg protein-1 and none respectively). 7. Methylene blue decomposed 2-NP and P2N at rates of 11 +/- 3 and 192 +/- 4 pmol nitrite x min-1 x nmol, methylene blue-1 respectively. The dye also enhanced NO2- formation from P2N and 2-NP in the presence of hepatocytes or serum proteins, with a concomitant enhancement of both 2-NP and P2N toxicity. 8. The results presented report species differences in the denitrification rate of 2-NP and highlight the crucial nitro-aci tautomerism of 2-NP as a pivotal determinant of 2-NP toxicity.

Secretoneurin: a market in rat hippocampal pathways

Secretoneurin is a 33-amino acid peptide, generated in brain by proteolytic processing of secretogranin II. The distribution of secretoneurin-like immunoreactivity and secretogranin II mRNA was investigated in the hippocampus of the rat. Secretogranin II mRNA was found in high concentrations throughout the granule cell and pyramidal cell layers and in many local neurons, notably in the hilus of the dentate gyrus. The general distributional pattern of secretoneurin-like immunoreactivity was characterized by a prominent staining in the area of the terminal field of mossy fibers with an obvious staining in the infrapyramidal area of CA3 and a strongly immunopositive band in the inner third of the molecular layer of the dentate gyrus. Lesions of the granule cells by local injection of colchicine significantly reduced secretoneurin-like immunoreactivity in the terminal field of mossy fibers, but not in the inner molecular layer of the dentate gyrus. On the other hand, destruction of interneurons of the dentate gyrus (mossy cells and certain gamma-aminobutyricacid-ergic interneurons) by kainic acid-induced seizures was associated with a reduction of secretoneurin-like immunoreactivity in the inner molecular layer of the dentate gyrus. However, 30 days after kainic acid-induced seizures, a strongly secretoneurin-immunoreactive band reappeared in this area, which at this late time point is due to sprouting of mossy fibers collaterals. Our experiments suggest a widespread distribution of secretoneurin-like immunoreactivity in neurons of the hippocampal formation with a preferential localization in excitatory pathways including associational/commissural fibers originating from secretoneurin-containing mossy cells.

Troglitazone inhibits fatty acid oxidation and esterification, and gluconeogenesis in isolated hepatocytes from starved rats

The effects of troglitazone and pioglitazone on glucose and fatty acid metabolism were studied in hepatocytes isolated from 24-h-starved rats. These thiazolidinediones inhibited long-chain fatty acid (oleate) oxidation and produced a very oxidized mitochondrial redox state. By contrast, thiazolidinediones did not affect the rate of medium-chain fatty acid (octanoate) oxidation or the activity of mitochondrial carnitine palmitoyltransferase (CPT) I. Thiazolidinediones inhibited selectively triglyceride synthesis but not phospholipid synthesis. The combined inhibition of oleate oxidation and esterification by troglitazone was due to a noncompetitive inhibition of mitochondrial and microsomal long-chain acyl-CoA synthetase (ACS) activities. It was suggested that troglitazone must be metabolized into its sulfo-conjugate derivative in liver cells to inhibit mitochondrial and microsomal ACS activities. Thiazolidinediones inhibited glucose production from lactate/pyruvate or from alanine. Analysis of gluconeogenic metabolite concentrations suggested that troglitazone would inhibit gluconeogenesis at the level of pyruvate carboxylase and glyceraldehyde-3-phosphate dehydrogenase reactions. It was concluded that 1) at a similar concentration, troglitazone was more efficient than pioglitazone to inhibit fatty acid metabolism and gluconeogenesis and 2) the inhibition of gluconeogenesis by troglitazone could be the result of the inhibition of long-chain fatty acid oxidation (decrease in acetyl-CoA, NADH-to-NAD+, and ATP-to-ADP ratios).

Cyclic AMP and fatty acids increase carnitine palmitoyltransferase I gene transcription in cultured fetal rat hepatocytes

In the rat, the gene for liver mitochondrial carnitine palmitoyltransferase I (CPT I), though dormant prior to birth, is rapidly activated postnatally. We sought to elucidate which hormonal and/or nutritional factors might be responsible for this induction. In cultured hepatocytes from 20-day-old rat fetus, the concentration of CPT I mRNA, which initially was very low, increased dramatically in a dose-dependent manner after exposure of the cells to dibutyryl cAMP (Bt2cAMP). Similar results were obtained when long-chain fatty acids (LCFA), but not medium-chain fatty acids, were added to the culture medium. The effects of Bt2cAMP and LCFA were antagonized by insulin, also dose dependently. In contrast, CPT II gene expression, which was already high in fetal hepatocytes, was unaffected by any of the above manipulations. Bt2cAMP stimulated CPT I gene expression even when endogenous triacylglycerol breakdown was suppressed by lysosomotropic agents suggesting that the actions of cAMP and LCFA were distinct. Moreover, half-maximal concentrations of Bt2cAMP and linoleate produced an additive effect CPT I mRNA accumulation. While linoleate and Bt2cAMP stimulated CPT I gene transcription by twofold and fourfold, respectively, the fatty acid also increased the half-life of CPT I mRNA (50%). When hepatocytes were cultured in the presence of 2-bromopalmitate, (which is readily converted by cells into its non-metabolizable CoA ester) CPT I mRNA accumulation was higher than that observed with oleate or linoleate. Similarly, the CPT I inhibitor, tetradecylglycidate, which at a concentration of 20 microM did not itself influence the CPT I mRNA level, enhanced the stimulatory effect of linoleate. The implication is that induction of the CPT I message by LCFA does not require mitochondrial metabolism of these substrates; however, formation of their CoA esters is a necessary step. Unlike linoleate, the peroxisome proliferator, clofibrate, increased both CPT I and CPT II mRNA levels and neither effect was offset by insulin. It thus appears that the mechanism of action of LCFA differs from that utilized by clofibrate, which presumably works through the peroxisome proliferator activated receptor. We conclude that the rapid increase in hepatic CPT I mRNA level that accompanies the fetal to neonatal transition in the rat is triggered by the reciprocal change in circulating insulin and LCFA concentrations, coupled with elevation of the liver content of cAMP.

Catalysis of nitro-aci tautomerism of the genotoxicant 2-nitropropane by cytosol from rodent and human liver

2-Nitropropane (2-NP) is a genotoxicant and hepatocarcinogen in rodents. Conversion to propane 2-nitronate (P2N), the anion of the tautomeric aci form of 2-NP, seems to be a pivotal part of the mechanism by which 2-NP causes its toxicity. We tested the hypothesis that the tautomeric equilibrium is influenced by enzymes in the liver, the target organ of 2-NP toxicity. Rat or mouse hepatocytes were incubated with 2-NP, P2N or the 2-NP isotopomer 2-deutero 2-nitropropane (2H-2-NP), which equilibrates with P2N much more slowly than 2-NP. Tautomers were analyzed by HPLC. The rates of conversion of 2-NP to P2N expressed as nmol P2N x (10(6) cells/ml)-1 x min-1 were 4.0 and 4.2 in the presence of hepatocytes from rats or mice, respectively, and 2.6 in the absence of cells. Production of 2-NP to P2N expressed as nmol 2-NP x (10(6) cells/ml)-1 x min-1 was increased from 6.1 in the absence of cells to 11.9 or 9.9 in the presence of hepatocytes from rats or mice, respectively. The rate of formation of P2N from 2H-2-NP as compared to 2-NP was characterised by a primary isotope effect of 3.4 and 3.8 in hepatocytes from rats and mice, respectively, contrasting with a value of 9.6 measured in medium omitting cells. When 2-NP was incubated with subfractions of rodent or human liver homogenate, production of P2N by cytosol was between 7.3 (mouse liver) and 28.1 times (human liver) higher than that observed in microsomes. Similarly generation of 2-NP from P2N by cytosol exceeded that in microsomes by a factor of two. Tautomerism in heat-activated cytosol, mitochondria or microsomes was not different from that in buffer only. The results suggest that the nitro-aci tautomerism of secondary nitroalkanes is catalysed by a hepatic enzyme which resides predominantly in the cytosol and may thus contribute to the generation of the toxic species via which 2-NP exerts its toxicity.

Metabolism of the genotoxicant 2-nitropropane to a nitric oxide species

The mechanisms by which the paint constituent 2-nitropropane (2-NP) exerts genotoxicity and hepatocarcinogenicity are poorly understood. The hypothesis was tested that nitric oxide (NO) is a hepatic metabolic intermediate generated from 2-NP and/or its anionic tautomer propane 2-nitronate (P2N). Incubations of liver microsomes from phenobarbital-pretreated rats or mice with 2-NP or P2N gave spectra with Soret maxima at 448 nm which indicated the presence of a ferrous-NO complex. Levels of 3':5'-cyclic guanosine monophosphate (cGMP) and nitrite were measured by ELISA assay and HPLC, respectively, in freshly isolated mouse hepatocytes. Levels of cGMP generated within 3 h in cells by 2-NP, P2N (5 mM each) or the diethylamine/NO complex [Et2NNO(N==O)]Na (0.6 mM), an NO precursor, were 6, 15 and 34 times, respectively, those seen in control hepatocytes. Production of cGMP following treatment with 2-NP was linear with time of incubation; cGMP generation from P2N reached its peak already after 1 h. cGMP levels observed in incubates with 1-nitropropane and 2-deutero 2-nitropropane (5 mM), 2-NP isomers devoid of genotoxic properties, were significantly lower than those seen in the presence of 2-NP. Inclusion in the incubate of methylene blue, which inhibits NO-mediated reactions, decreased cGMP formation in hepatocytes with [Et2NNO(N==O)]Na, but increased it in cells with 2-NP or P2N. The production of nitrite from 2-NP, P2N or [Et2NNO(N==O)]Na mirrored cGMP formation. The results suggest that 2-NP and its nitronate generate an NO species in cells which may mediate, or contribute to, 2-NP genotoxicity.

Determinants of patency after percutaneous angioplasty and atherectomy of occluded superficial femoral arteries

BACKGROUND

Patients undergoing percutaneous recanalization of chronically occluded superficial femoral arteries were studied to determine which factors correlated with 1-year patency. Immediate change in ankle:brachial index (ABI), length of occlusion, tibial run-off, and the performance of supplemental catheter atherectomy were evaluated.

METHODS

Eligible patients had at least one patient tibial run-off vessel and the absence of limb-threatening ischemia. Recanalization was performed via passage of a guidewire followed by balloon angioplasty. Tibial run-off was scored based on a modification of the angiogram scoring system of the Society for Vascular Surgery and the International Society for Cardiovascular Surgery. Supplemental transcutaneous extraction catheter atherectomy was randomly assigned to a sub-group of patients after initial experience with the recanalization technique. Clinical follow-up was employed to determine patency.

RESULTS

Forty-two of 57 attempts (74%) at recanalization were immediately successful. Overall 1-year patency was 40% in 40 limbs that could be followed. In limbs with balloon angioplasty alone (n = 23), patency was 43% compared with 35% in those having supplemental atherectomy. Tibial run-off did not vary significantly between patent and occluded groups. When ABI increased by 0.3 or more, patency was 56% compared with 26% when the ABI increase was less than or equal to 0.1 (P = 0.13). Occlusion length averaged 18.1 +/- 10.6 cm for all limbs and did not vary significantly between early successes and failures. Limbs with short occlusions (less than or equal to 5 cm, n = 8) had 63% patency compared with 38% patency for limbs with long occlusions (greater than 25 cm, n = 16), but the difference was not significant by analysis of variance.

CONCLUSIONS

An initial change in ABI was most predictive for patency, whereas no correlation with tibial run-off was demonstrated. Atherectomy did not increase patency. Short occlusions were more likely to remain patent than long ones, but overall patency was lower than described in other series.

Propane 2-nitronate is the major genotoxic form of 2-nitropropane

The mutagenicity of 2-nitropropane in Salmonella typhimurium (strain TA100) was proportional to the pH (range 6.1-9.1) of the medium used for pre-incubation of the agent and for incubation of the agent with the Salmonella. The mutagenicity correlated with an enhanced rate of tautomerase to propane 2-nitronate at relatively high pH as measured by high performance liquid chromatography. Both the mutagenicity in Salmonella typhimurium (strains TA100 and TA102) and the rate of tautomerisation to the nitronate was lower with 2-deutero-2-nitropropane than with non-deuterated 2-nitropropane. Furthermore, 2-deutero-2-nitropropane was less potent in the induction of unscheduled DNA synthesis in rat hepatocytes over a 4-h period. Propane 2-nitronate therefore appears to be pivotal in the causation of the genetic toxicity of 2-nitropropane. The presence of hepatocytes enhanced nitronate production from 2-nitropropane suggesting a contribution from hepatic enzymes in the tautomerisation reaction.

Hepatic ketogenesis in newborn pigs is limited by low mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase activity

In newborn-pig hepatocytes, the rate of oleate oxidation is extremely low, despite a very low malonyl-CoA concentration. By contrast, the sensitivity of carnitine palmitoyltransferase (CPT) I to malonyl-CoA inhibition is high, as suggested by the very low concentration of malonyl-CoA required for 50% inhibition of CPT I (IC50). The rates of oleate oxidation and ketogenesis are respectively 70 and 80% lower in mitochondria isolated from newborn-pig liver than from starved-adult-rat liver mitochondria. Using polarographic measurements, we showed that the oxidation of oleoyl-CoA and palmitoyl-L-carnitine is very low when the acetyl-CoA produced is channelled into the hydroxymethylglutaryl-CoA (HMG-CoA) pathway by addition of malonate. In contrast, the oxidation of the same substrates is high when the acetyl-CoA produced is directed towards the citric acid cycle by addition of malate. We demonstrate that the limitation of ketogenesis in newborn-pig liver is due to a very low amount and activity of mitochondrial HMG-CoA synthase as compared with rat liver mitochondria, and suggest that this could promote the accumulation of acetyl-CoA and/or beta-oxidation products that in turn would decrease the overall rate of fatty acid oxidation in newborn- and adult-pig livers.

Identification of drug glucuronides in human urine by RP-HPLC after derivatization

A method for the identification of four types of drug glucuronides in human urine is presented. The approach involves solid-phase extraction (C18 columns) from acidified human urine and subsequent methylation and acetylation of the extracted drug glucuronides to triacetyl methyl derivatives. These derivatives were identified by RP-HPLC by comparison with synthesized authentic reference compounds. The scope of the method was demonstrated by identification of glucuronides formed by metabolism of clofibrate, phenazone, disulfiram and sulfamethoxazole in urine samples of two male volunteers.

Evidence for an impaired long-chain fatty acid oxidation and ketogenesis in Fao hepatoma cells

Fatty acid metabolism has been studied in Fao rat hepatoma cells. In basal conditions of culture, [1-14C]oleate is mainly esterified (85% of oleate uptake) in Fao cells, phospholipids being the most important esterified products (60% of oleate esterified). Addition of N6,O2'-dibutyryl-adenosine 3',5'-monophosphate (0.1 mM) in Fao cells does not change the metabolic fate of oleate whereas it induces gluconeogenesis and phosphoenolpyruvate carboxykinase mRNA accumulation. It is shown that the limitation of oleate oxidation is located at the level of the entry into mitochondria since octanoate is actively oxidized in Fao cells. Neither the activities of carnitine palmitoyltransferase (CPT) I and II nor the CPT II protein amount are affected by cAMP addition. The limitation of oleate oxidation in Fao cells results from (a) a high rate of lipogenesis and a high malonyl-CoA concentration, (b) a CPT I very sensitive to malonyl-CoA inhibition. The presence of an active oleate oxidation in mitochondria isolated from Fao cells confirms that CPT I is the limiting step of oleate oxidation. Moreover, Fao cells are unable to perform ketogenesis. This particular feature results from a specific deficiency in mitochondrial hydroxymethylglutaryl-CoA synthase protein, activity and gene expression. The metabolic characteristics observed in Fao cells could be a common feature in hepatoma cell lines with regard to the low capacity for long-chain fatty acid oxidation and ketone body production observed in the rat H4IIE and the human HepG2 cells.

Acetoxime is metabolized by human and rodent hepatic cytochrome P450 enzymes to the genotoxicant and carcinogen propane 2-nitronate

The hepatocarcinogenicity of acetoxime has been tentatively linked with its metabolic oxidation to the potent genotoxicant and carcinogen propane 2-nitronate (P2-N). In order to test the hypothesis that acetoxime is metabolized to P2-N, the oxime (20 mM) was incubated with liver microsomes from mice, rats and two humans. Ion-pair HPLC analysis of the incubates afforded a peak that co-eluted with P2-N. P2-N exists in tautomeric equilibrium with 2-nitropropane (2-NP). Samples of the microsomal incubates, which had been adjusted to pH 5.5 and kept for 24 h in order to allow maximal tautomeric equilibration of P2-N to 2-NP to occur, were extracted with hexane. GLC analysis of the extracts yielded a peak that co-eluted with 2-NP, and gave a mass spectrum identical to that of authentic 2-NP. The metabolite peak obtained on HPLC was isolated and its hexane extract contained also 2-NP when investigated by GLC. P2-N was found by HPLC in the urine of rats that had received acetoxime (3.36 mmol/kg i.p.). Hexane extracts of urine samples, which had been adjusted to pH 5.5 and left for 24 h, contained 2-NP as demonstrated by GLC analysis. The results are consistent with the suggestion that the toxicity of acetoxime is associated with its biotransformation to P2-N.

Effects of isomazole on force of contraction and phosphodiesterase isoenzymes I-IV in nonfailing and failing human hearts

The phosphodiesterase (PDE) inhibitor isomazole increased the force of contraction to 278.3 +/- 89.1% (n = 7) of the predrug value in ventricular trabeculae carneae isolated from nonfailing human hearts. This effect can be attributed mainly to a PDE III or a combined PDE III/IV inhibition since at the concentration of the maximal positive inotropic effect of isomazole, PDE III and PDE IV were completely inhibited. In explanted failing human hearts (end-stage myocardial failure, NYHA IV), isomazole increased the force of contraction only marginally to 110.1 +/- 10.7% of the predrug value. The lack of a distinct positive inotropic efficacy of isomazole in failing human hearts could not be explained by an impairment of PDE inhibition since the properties of the PDE I-IV isoenzymes separated by DEAE-Sepharose chromatography and the inhibitory effects of isomazole did not differ in both preparations. The positive inotropic effect of the beta-adrenoceptor agonist isoprenaline was also reduced in failing hearts. However, in the presence of isomazole, the diminished positive inotropic effect of isoprenaline was restored to values obtained with isoprenaline alone in nonfailing hearts. Thus, the decreased effect of inotropic drugs like isoprenaline or isomazole in preparations from failing human heart might be explained mainly by a diminished cAMP formation due to a defect in receptor-adenylate cyclase coupling.

[The pharmacokinetics of antilipemic agents. 8. Unequivocal characterization of ciprofibrate-O-beta-d-glucuronide]

After an oral single dose Ciprofibrate (1) is eliminated mainly (greater than 90%) as its glucuronide renally and to a small amount on the biliary route. This conjugate could be extracted out of the urine of volunteers. By methylation of the carboxy group and acetylation of the three hydroxy groups of the glucuronic acid the hydrophobic methyl-(2,3,4-tri-O-acetyl-beta-D-glucopyrano)-uronate was formed. This derivative could be identified unequivocally by HPLC using the reference substance which can be obtained easily. Due to the chirality of 1 its glucuronide and the corresponding hydrophobe derivative (melting range 67-78 degrees C) are a mixture of diastereomeres. The latter could be separated analytically into the diastereomeres using a cyclobond I-column.

Effects of gonadotropins, insulin and insulin-like growth factor I on ovarian oxytocin and progesterone production

Oxytocin is produced in the granulosa-derived cells of the ruminant corpus luteum where its gene is dramatically up-regulated within days of ovulation. Regulation of these processes is poorly understood but oxytocin release can be increased by insulin, insulin-like growth factor I (IGF-I), and gonadotropins. Here we have assessed interactions between these regulatory systems. Follicle-stimulating hormone (FSH), luteinizing hormone (LH) and human chorionic gonadotropin (hCG) caused dose-dependent release of oxytocin from bovine granulosa cells cultured in medium containing 100 ng/ml insulin. The gonadotropins also increased oxytocin mRNA levels and their effects were mimicked by forskolin. The effects of these stimuli on oxytocin and progesterone release were synergistically increased by insulin or IGF-I. Binding studies revealed separate binding sites with characteristics of insulin and IGF-I receptors. Insulin potentiated the effects of hCG and forskolin on oxytocin mRNA levels and release of oxytocin and progesterone in cells from follicles containing greater than 50 ng/ml estradiol. In cells from follicles containing less than 5 ng/ml estradiol these stimuli had little effect on oxytocin release although progesterone release was synergistically increased by insulin and forskolin. The data suggest that gonadotropins regulate oxytocin synthesis and release and that these effects are amplified by insulin or IGF-I acting via their own receptors. Changes associated with maturation of the target cells in vitro appear prerequisite for oxytocin production in response to increased cAMP levels in the presence of insulin or IGF-I.

Regulation of fatty-acid metabolism by pancreatic hormones in cultured human hepatocytes

The effects of pancreatic hormones and cyclic AMP on long-chain fatty-acid metabolism were investigated in human hepatocytes isolated from 12 liver biopsy specimens and cultured for 4 days in an insulin-free medium. Glucagon (10(-6) mol/L) increased endogenous ketone body production by 150%. This resulted from alterations in the partition of long-chain fatty acids from esterification toward oxidation. Glucagon or cyclic AMP enhanced (14C) oleate oxidation (basal = 45.8% +/- 5.0%; glucagon = 66.8% +/- 5.3%; cyclic AMP = 67.6% +/- 5.0% of metabolized oleate) at the expense of oleate esterification. Insulin (10(-7) mol/L) antagonized the glucagon-induced oleate oxidation. After 24 hr in basal culture conditions, the rate of lipogenesis decreased to the same low rate as in glucagon-treated cells. The presence of insulin did not restore a high rate of lipogenesis. These results are the first direct evidence of a control of ketone body production by glucagon in the human liver.

Effects of carbachol and (-)-N6-phenylisopropyladenosine on myocardial inositol phosphate content and force of contraction

1. The effects of carbachol and the A1-adenosine receptor agonist (-)-N6-phenylisopropyladenosine (PIA) on force of contraction and inositol lipid metabolism were studied in electrically driven left auricles and papillary muscles isolated from guinea-pig hearts. Both carbachol and PIA (0.01-10 microM) had concentration-dependent negative inotropic effects in auricles. In papillary muscles PIA had no inotropic effect. Carbachol also had no inotropic effect at low concentrations (0.01-1 microM) but at 10-100 microM it exerted a slight positive inotropic effect. 2. In auricles and papillary muscles both carbachol and PIA concentration-dependently increased inositol trisphosphate (IP3; significant at 1 microM). Accordingly phosphatidylinositol bisphosphate (PIP2), the precursor of IP3, was reduced. All effects of carbachol and PIA were antagonized by atropine (10 microM) and 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 20 microM) respectively, indicating receptor-mediated effects. 3. In auricles the negative inotropic effects of carbachol and PIA preceded the increase in IP3. 4. In papillary muscles the increase in IP3 preceded the slight positive inotropic effect of carbachol, indicating that the M-cholinoceptor-mediated increase in IP3 and force of contraction may be related. However, PIA showed a comparable increase in IP3 but no inotropic effect, indicating a dissociation between those parameters. 5. In conclusion, in previous studies a close relation between increases in IP3 and force of contraction has been shown after alpha 1-adrenoceptor stimulation. The present study with carbachol supports this view. However, the present data for PIA could not show such a close relationship, questioning the role of IP3 as an endogenous regulator of force of contraction.

Positive inotropic effect of carbachol and inositol phosphate levels in mammalian atria after pretreatment with pertussis toxin

The m-cholinoceptor agonist carbachol elicits a negative inotropic effect in mammalian atria. Pretreatment with pertussis toxin converts the negative to a positive inotropic effect. In this study we investigated the time course of the effects of carbachol on force of contraction and phosphoinositide products in electrically driven left auricles from guinea pig hearts after pretreatment with pertussis toxin (180 micrograms/kg i.v.; 24 hr). Inositol phosphates and phosphatidylinositols were labeled with [3H]inositol and separated with high-performance liquid chromatography and thin-layer chromatography, respectively. All experiments were performed in the presence of LiCl (10 mmol/l). The positive inotropic effect of carbachol (10 mumol/l) began within 2 min and was maximal within 15 min. Inositol 1,4,5-trisphosphate rose within 1 min followed by an increase in inositol 1,3,4,5-tetrakisphosphate, inositol 1,3,4-trisphosphate, inositol 1,4-bisphosphate and inositol 1-phosphate beginning within 2 min. It is concluded that the carbachol-induced positive inotropic effect is associated with an increase in the presumed second messengers inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate. Since the increase in inositol 1,4,5-trisphosphate precedes the increase in force of contraction, it may initiate the positive inotropic effect. The increase in inositol 1,3,4,5-tetrakisphosphate may be involved in maintaining the positive inotropic effect of carbachol.

Evidence that the sensitivity of carnitine palmitoyltransferase I to inhibition by malonyl-CoA is an important site of regulation of hepatic fatty acid oxidation in the fetal and newborn rabbit. Perinatal development and effects of pancreatic hormones in cultured rabbit hepatocytes

The temporal changes in oleate oxidation, lipogenesis, malonyl-CoA concentration and sensitivity of carnitine palmitoyltransferase I (CPT 1) to malonyl-CoA inhibition were studied in isolated rabbit hepatocytes and mitochondria as a function of time after birth of the animal or time in culture after exposure to glucagon, cyclic AMP or insulin. (1) Oleate oxidation was very low during the first 6 h after birth, whereas lipogenesis rate and malonyl-CoA concentration decreased rapidly during this period to reach levels as low as those found in 24-h-old newborns that show active oleate oxidation. (2) The changes in the activity of CPT I and the IC50 (concn. causing 50% inhibition) for malonyl-CoA paralleled those of oleate oxidation. (3) In cultured fetal hepatocytes, the addition of glucagon or cyclic AMP reproduced the changes that occur spontaneously after birth. A 12 h exposure to glucagon or cyclic AMP was sufficient to inhibit lipogenesis totally and to cause a decrease in malonyl-CoA concentration, but a 24 h exposure was required to induce oleate oxidation. (4) The induction of oleate oxidation by glucagon or cyclic AMP is triggered by the fall in the malonyl-CoA sensitivity of CPT I. (5) In cultured hepatocytes from 24 h-old newborns, the addition of insulin inhibits no more than 30% of the high oleate oxidation, whereas it stimulates lipogenesis and increases malonyl-CoA concentration by 4-fold more than in fetal cells (no oleate oxidation). This poor effect of insulin on oleate oxidation seems to be due to the inability of the hormone to increase the sensitivity of CPT I sufficiently. Altogether, these results suggest that the malonyl-CoA sensitivity of CPT I is the major site of regulation during the induction of fatty acid oxidation in the fetal rabbit liver.

Evidence for the existence of inositol tetrakisphosphate in mammalian heart. Effect of alpha 1-adrenoceptor stimulation

The time course of the effects of phenylephrine (10 mumol/l) on force of contraction and on inositol phosphates in electrically driven left auricles from rat hearts labeled with [3H]inositol was studied. All experiments were performed in the presence of propranolol (1 mumol/l) and LiCl (10 mmol/l). Products measured after separation with high-performance liquid chromatography were inositol 1-phosphate (1-IP1), inositol 1,4-bisphosphate (1,4-IP2), inositol 1,3,4-trisphosphate (1,3,4,-IP3), inositol 1,4,5-trisphosphate (1,4,5-IP3), and inositol 1,3,4,5-tetrakisphosphate (1,3,4,5-IP4). All inositol phosphates increased after stimulation with phenylephrine. 1,4,5-IP3 was the first compound to rise maximally within 30 seconds; this rise was followed by an increase in 1,3,4,5-IP4 and 1,4-IP2 beginning within 2 minutes. The increase in 1,3,4-IP3 and 1-IP1 was slower and did not reach steady state within 15 minutes. The positive inotropic effect of phenylephrine was maximal after 5 minutes. It is concluded that the increase in the presumed second messengers 1,4,5-IP3 and 1,3,4,5-IP4 coincides with the positive inotropic effect after alpha 1-adrenoceptor stimulation. Since the increase in 1,4,5-IP3 precedes the increase in force of contraction, 1,4,5-IP3 may initiate the positive inotropic effect of alpha 1-adrenoceptor agonists and 1,3,4,5-IP4 maintains the increase in force of contraction.

On the mechanism of positive inotropic effects of alpha-adrenoceptor agonists

The positive inotropic effect of the alpha 1-adrenoceptor agonist phenylephrine is accompanied by an increase in the presumed second messengers inositol 1,4,5-trisphosphate (1,4,5-IP3) and inositol 1,3,4,5-tetrakisphosphate (1,3,4,5-IP4). Both 1,4,5-IP3 and 1,3,4,5-IP4 sensitize myocardial contractile proteins in chemically skinned fibers. In addition to the Ca++ releasing effect of 1,4,5-IP3 from the sarcoplasmic reticulum the Ca++-sensitizing effect of the inositol phosphates may play a role in alpha 1-adrenergic positive inotropism. In isolated heart muscle preparations from patients with endstage heart failure (due to dilated cardiomyopathy) beta-adrenergic as well as alpha 1-adrenergic effects are reduced compared to preparations from healthy hearts. The reduced beta-adrenergic effects can in part be explained by an increased content of signal transducing G1-proteins. It is tempting to investigate whether other G proteins are also altered in severe congestive heart failure.

Induction of ketogenesis and fatty acid oxidation by glucagon and cyclic AMP in cultured hepatocytes from rabbit fetuses. Evidence for a decreased sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition after glucagon or cyclic AMP treatment

The effects of pancreatic hormones and cyclic AMP on the induction of ketogenesis and long-chain fatty acid oxidation were studied in primary cultures of hepatocytes from fetal and newborn rabbits. Hepatocytes were cultivated during 4 days in the presence of glucagon (10(-6) M), forskolin (2 x 10(-5) M), dibutyryl cyclic AMP (10(-4) M), 8-bromo cyclic AMP (10(-4) M) or insulin (10(-7) M). Ketogenesis and fatty acid metabolism were measured using [1-14C]oleate (0.5 mM). In hepatocytes from fetuses at term, the rate of ketogenesis remained very low during the 4 days of culture. In hepatocytes from 24-h-old newborn, the rate of ketogenesis was high during the first 48 h of culture and then rapidly decreased to reach a low value similar to that measured in cultured hepatocytes from term fetuses. A 48 h exposure to glucagon, forskolin or cyclic AMP derivatives is necessary to induce ketone body production in cultured fetal hepatocytes at a rate similar to that found in cultured hepatocytes from newborn rabbits. In fetal liver cells, the induction of ketogenesis by glucagon or cyclic AMP results from changes in the partitioning of long-chain fatty acid from esterification towards oxidation. Indeed, glucagon, forskolin and cyclic AMP enhance oleate oxidation (basal, 12.7 +/- 1.6; glucagon, 50.0 +/- 5.5; forskolin, 70.6 +/- 5.4; cyclic AMP, 77.5 +/- 3.4% of oleate metabolized) at the expense of oleate esterification. In cultured fetal hepatocytes, the rate of fatty acid oxidation in the presence of cyclic AMP is similar to the rate of oleate oxidation present at the time of plating (85.1 +/- 2.6% of oleate metabolized) in newborn rabbit hepatocytes. In hepatocytes from term fetuses, the presence of insulin antagonizes in a dose-dependent fashion the glucagon-induced oleate oxidation. Neither glucagon nor cyclic AMP affect the activity of carnitine palmitoyltransferase I (CPT I). The malonyl-CoA concentration inducing 50% inhibition of CPT I (IC50) is 14-fold higher in mitochondria isolated from cultured newborn hepatocytes (0.95 microM) compared with fetal hepatocytes (0.07 microM), indicating that the sensitivity of CPT I decreases markedly in the first 24 h after birth. The addition of glucagon or cyclic AMP into cultured fetal hepatocytes decreased by 80% and 90% respectively the sensitivity of CPT I to malonyl-CoA inhibition. In the presence of cyclic AMP, the sensitivity of CPT I to malonyl-CoA inhibition in cultured fetal hepatocytes is very similar to that measured in cultured hepatocytes from 24-h-old newborns.

Octanoate metabolism in isolated hepatocytes and mitochondria from fetal, newborn and adult rabbit. Evidence for a high capacity for octanoate esterification in term fetal liver

Ketogenesis from endogenous fatty acids or from exogenous octanoate has been studied in isolated hepatocytes from fetal. 24-h-old newborn and adult rabbit. In fed adult rabbits, endogenous ketogenesis is low and increases sixfold in the presence of 2 mM octanoate. At birth, endogenous ketogenesis is low and markedly increases 24 h after birth but, in both cases, the addition of 2 mM octanoate does not increase the rates of ketone body production. Hepatocytes isolated from 24-h-old newborn or fed adult rabbits and incubated with [1-14C]octanoate show a preferential channeling of fatty acid into oxidation (84-92% of octanoate metabolized). In contrast, esterification represents 43% of the amount of octanoate metabolized at birth. Chromatographic analysis of labelled triacylglycerols shows that 76 +/- 2% of labelled fatty acids are identified as octanoate and all of the radioactivity in the octanoate peak is due to the carboxyl carbon. In hepatocytes from term fetus, the low capacity for octanoate oxidation is associated with a high capacity for esterification, whatever the octanoate concentration in the medium. Octanoate activated to octanoyl-CoA in the cytosol of fetal hepatocyte is not oxidized in the mitochondria since carnitine acyltransferase I has a low activity at birth in the rabbit. This suggests that only a part of the octanoate pool is activated outside the mitochondria. Factors involved in the direct esterification of octanoate into triacylglycerols in term fetal hepatocytes are discussed.

Evidence for alpha 1-adrenoceptor-mediated increase of inositol trisphosphate in the human heart

In human-isolated ventricular myocardium the alpha 1-adrenoceptor agonist phenylephrine has a positive inotropic effect but its mechanism is largely unknown. We studied the effects of phenylephrine in trabeculae isolated from three nonfailing human hearts. We found that the force of contraction rose concentration-dependently (1-300 mumol/L), maximally, to about 235% of control (at 100 mumol/L). The inositol phosphates were increased to 195-262%, whereas the phosphatidylinositol phosphate and phosphatidylinositol bisphosphate decreased to 69-73% of control. The present results suggest that the alpha 1-adrenoceptor-mediated increase in inositol trisphosphate and the positive inotropic effect may be causally related in the normal human heart.

Premature appearance of gluconeogenesis and fatty acid oxidation in the liver of the postterm rabbit fetus

The metabolic consequences of a prolonged gestation (35 vs 32 days) have been studied in the rabbit fetus. Gestation was prolonged by daily subcutaneous injections of progesterone (1.5 mg.kg-1) from day 28 to 34. In control animals, progesterone was injected from day 25 or 28 to day 31 of gestation. When the capacities for gluconeogenesis and fatty acid oxidation, measured on isolated hepatocytes, are normally low in the term control fetus and increase only within the first 24 h after birth, these capacities appear high in the postmature fetus. The rate of glucose production from lactate is 4-fold higher in the postmature fetus than in the normal term fetus. The rate of ketone body production from oleate is also 5-fold higher in the postmature fetus, which results from a switch on of the partition of oleate into esterification and oxidation: 8% of [1-14C]oleate is oxidized in term fetus hepatocytes, but 34% in postmature fetus hepatocytes. As a similar rate of lipogenesis takes place in both stages, this metabolic change could be explained by a 5-fold lower sensitivity of carnitine palmitoyltransferase I to the inhibition by malonyl-coenzyme A. Postmaturity decreases plasma insulin concentrations by 45% and increases plasma glucagon concentrations by 50% which, in turn, induces a 3-fold decrease in the plasma insulin:glucagon molar ratio. As previously shown in fasted or diabetic adult rat, this hormonal change might be a likely candidate for an enhancement of gluconeogenic and ketogenic capacity in the liver of the postterm rabbit fetus.

Regulation of fatty acid oxidation in isolated hepatocytes and liver mitochondria from newborn rabbits

The changes in long-chain fatty acid oxidation during the first 24 h after birth were studied in isolated rabbit hepatocytes and liver mitochondria. The eightfold increase in this oxidation which occurs in hepatocytes between birth and 24 h was not triggered by a concomitant decrease in long-chain fatty acid esterification. Indeed, in isolated hepatocytes from 24-h-old rabbits, the 75% inhibition of the oxidation by 2-tetradecylglycidic acid, resulted in a total redirection of oleate metabolized towards triacylglycerol synthesis. Polarographic measurements of mitochondrial respiration showed that oxidative phosphorylation and respiratory chain capacity were fully functional at birth. By contrast, in liver mitochondria isolated from newborn rabbits, the rate of oxygen consumption from palmitoyl-L-carnitine was 60% higher than from palmitoyl-CoA. Similarly palmitoyl-CoA oxidation was increased 1.5-fold in isolated mitochondria from 24-h-old rabbits. These results were in agreement with the twofold increase in the activity of hepatic carnitine palmitoyltransferase I between birth and 24 h. However it is unlikely that the twofold increase in this enzyme activity totally explained the eightfold increase in long-chain fatty acid oxidation in isolated newborn rabbit hepatocytes. It was shown that the rate of the oxidation in isolated hepatocytes was inversely related to the rate of lipogenesis. Nevertheless, malonyl-CoA concentration per se is probably not the factor involved in the regulation of the oxidation between birth and 24 h, since a 90% decrease in hepatic malonyl-CoA concentration was not associated with a stimulation of long-chain fatty acid oxidation. The more likely mechanism was the 30-fold decrease in the sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition.

Hepatic triglyceride hydrolysis and development of ketogenesis in rabbits

Ketogenesis from endogenous fatty acids or exogenous oleate plus carnitine has been studied in isolated hepatocytes from fetal, newborn, and 70-day-old rabbits. During the first 48 h after birth, hepatic triacylglycerol stores decrease by 80%. The hydrolysis of hepatic triacylglycerol stores has been studied in isolated hepatocytes from 24-h-old fasting rabbits by using lysosomal acid lipase inhibitors and lysosomotropic agents. Their addition decreases the rates of ketone body production by 60-70%, suggesting that hepatic triacylglycerol hydrolysis proceeds via an acid lipase located in the lysosomes. Whereas the rates of ketogenesis from endogenous or exogenous fatty acids are very low in isolated hepatocytes from fetal rabbit, an eightfold increase in the rate of ketogenesis occurs between 6 and 24 h after birth; furthermore the hydrolysis of triacylglycerol stores is sufficient to support the ketogenic capacity in the hepatocytes isolated from 24-h-old rabbits. The emergence of ketogenesis in newborn rabbit hepatocytes is triggered by birth-associated factors rather than to an accurate stage of fetal maturation. Fatty acids are mainly oxidized in the mitochondria because peroxisomal oxidation does not exceed 10-15% of the overall beta-oxidation. Isolated hepatocytes incubated with [1-14C]oleate exhibit at birth a preferential channeling of fatty acid into esterification (93% of oleate metabolized) rather than into oxidation. Conversely oleate oxidation represents 50% of total oleate metabolized 24 h after birth. Factors involved in this switch on of the partition of oleate into esterification and oxidation during the 1st day after birth are discussed.