Acute myocardial ischemia: MR imaging with Mn-TP

Cardiac-gated magnetic resonance (MR) imaging was performed in rats to determine the effects of manganese ethylenediaminetetraphosphonate (TP). Ten normal rats received Mn-TP in a dose of 50 mumol/kg through a tail-vein injection. Spin-echo MR images were obtained before and every 10 minutes after Mn-TP injection for 1 hour. Cardiac signal intensity (SI) increased more than 70% after Mn-TP injection and remained nearly unchanged 1 hour after injection. Myocardial T1 was 517 +/- 49 msec in eight control rats and 282 +/- 61 msec (P less than .001) in six rats 81 +/- 0 minutes after injection. Nine rats underwent occlusion of the left anterior descending coronary artery prior to MR imaging. Images were obtained before and 15, 30, and 60 minutes after Mn-TP injection. In normal myocardium, SI increased up to 82% and remained elevated for 1 hour. In ischemic myocardium, SI rose 11%, leading to a marked contrast between the two tissue zones. T1 was also different in the two regions: In normal tissue, it was 206 msec +/- 54; in ischemic tissue, 338 +/- 82 (P less than .001). With T1-weighted MR imaging, Mn-TP showed a potential for delineating the jeopardized area after acute myocardial ischemia.     

Effect of dichloroacetate on gluconeogenesis in isolated rat hepatocytes

The effect of dichloroacetate on rates of gluconeogenesis was studied in isolated parenchymal cells obtained from the livers of normal fasted rats. Dichloroacetate significantly inhibited glucose formation from endogenous substrates and from added precursors (e.g., lactate, pyruvate, or glycerate) which enter the gluconeogenic pathway prior to the level of glyceraldehyde-3-phosphate dehydrogenase (GPDH). In contrast, dichloroacetate did not significantly affect glucose synthesis from precursors (e.g., fructose, or glycerol) which enter beyond the GPDH-catalyzed step. Lactate production from fructose or glycerol was unaffected by dichloroacetate. Inhibition of gluconeogenesis occurred regardless of the apparent effects of dichloro-acetate on the redox state of the cytosol. Dichloroacetate produced variable effects on the lactate-pyruvate substrate pair, while it consistently produced a more oxidized state in the β-hydroxybutyrate-acetoacetate couple. Unlike uncoupling agents, dichloroacetate reduced glucose synthesis without stimulating respiration or altering total adenine nucleotide levels or $\text{ATP}\text{ADP}$ ratios. Dichloroacetate did not affect the metabolism of lactate or pyruvate to CO₂ or glycogen. It did, however, significantly inhibit conversion by the cells of added lactate to pyruvate and glucose or of added pyruvate to lactate and glucose.     

Evaluation of dichloroacetate treatment in a murine model of hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease severely affecting liver and kidney and is caused by a deficiency in fumarylacetoacetate hydrolase (FAH). Administration of 2-(2-nitro-4-trifluoro-methylbenzyol)-1,3 cyclohexanedione (NTBC) improves the HT1 phenotype but some patients do not respond to NTBC therapy. The objective of the present study was to evaluate whether administration of dichloroacetate, an inhibitor of maleyl acetoacetate isomerase (MAAI) to FAH-knockout mice could prevent acute pathological injury caused by NTBC withdrawal. DCA (0.5 and 5g/L) was given in combination with a standard diet or with a tyrosine-restricted diet. With the low-tyrosine diet body weight loss and most of hepatic and renal injuries were prevented regardless the DCA dose. The administration of DCA with a standard diet did not prevent damage nor the oxidative stress response nor the AFP induction seen in FAH-knockout mice. DCA was shown to inhibit hepatic MAAI activity to 86% (0.5g/L) and 94% (5g/L) of untreated wild-type mice. Interestingly, FAH(-/-) mice deprived of NTBC (NTBC-OFF) and NTBC-treated FAH-knockout mice had similar low hepatic MAAI activity levels, corresponding to 10-20% of control. Thus the failure of DCA treatment in FAH(-/-) mice seems to be attributed to the residual MAAI activity, high enough to lead to FAA accumulation and HT1 phenotype.     

Plasma glutathione and cystathionine concentrations are elevated but cysteine flux is unchanged by dietary vitamin B-6 restriction in young men and women

Cysteine synthesis from homocysteine is catalyzed by two pyridoxal 5'-phosphate (PLP)-dependent enzymes. This suggests that vitamin B-6 status might affect cysteine and glutathione homeostasis, but it is unclear whether this occurs in humans. We assessed the effects of vitamin B-6 status on static and kinetic parameters of cysteine and glutathione metabolism in healthy female (n=5) and male (n=4) volunteers (20-30 y) before and after 4 wk of dietary vitamin B-6 restriction (<0.5 mg vitamin B-6/d). Rates of reactions related to cysteine metabolism were measured from blood sampled during primed, constant infusions of [(13)C(5)]methionine, [3-(13)C]serine, and [(2)H(2)]cysteine that were conducted after an overnight fast at baseline and after the dietary protocol. Vitamin B-6 restriction reduced the concentration of PLP (55.1+/- 8.3 vs. 22.6+/-1.3 nmol/L; P=0.004) and increased concentrations of cystathionine (124%; P<0.001) and total glutathione (38%; P<0.008) in plasma. Concentrations of plasma homocysteine, cysteine, cysteinylglycine, and C-reactive protein (an indicator of systemic inflammation) were not affected by dietary vitamin B-6 restriction. The rate of cysteine synthesis via transsulfuration was below detection limits in this protocol. Neither the fractional synthesis rate of cystathionine nor whole-body cysteine flux was affected by vitamin B-6 restriction. These data indicate that glutathione homeostasis is altered by dietary vitamin B-6 deficiency and appears to be unrelated to cysteine flux under conditions of minimal amino acid intake as evaluated in this study.     

Lipodystrophic diabetes mellitus. Investigations of lipoprotein metabolism and the effects of omega-3 fatty acid administration in two patients

We investigated the metabolic effects of omega-6 (safflower oil) and omega-3 (fish oil) fatty acid-enriched diets (65% carbohydrate, 20% fat) in two patients with a syndrome of diabetes mellitus, lipodystrophy, acanthosis nigricans, chylomicronemia, and abdominal pain. 3H-glycerol was used to evaluate triglyceride-rich lipoprotein-triglyceride (TRLP-TG) metabolism, and changes in glucose and insulin dynamics were also studied. On the omega-6 diet, both subjects demonstrated four- to five-times normal rates of TRLP-TG production and glycerol biosynthesis, and striking decrements in the fractional catabolic rate (FCR) for TRLP-TG and TRLP-particles. Both subjects had elevations in nonesterified fatty acid (NEFA) concentrations. In one patient, the omega-3 diet markedly decreased serum triglycerides and newly synthesized triglyceride glycerol production, in association with a fall in NEFA. In both subjects, plasma glycerol reutilization for triglyceride synthesis, normal on the omega-6 diet, was abolished on the omega-3 regimen. Plasma postheparin lipolytic activity was normal on both diets. On the omega-3 diet, xanthomas and hepatomegaly decreased and, in the patient who had no reduction in serum triglycerides, pancreatitis attacks virtually ceased. Mean 24-hour serum glucose levels were higher, and both basal and peak C-peptide responses to a carbohydrate meal were blunted on the omega-3 diet. One patient became ketonuric. We conclude the cause of hypertriglyceridemia in these patients was due to increased lipid synthesis and hypothesize that this is secondary to high plasma concentrations of NEFA. In addition, an omega-3 diet in these subjects inhibited insulin secretion and worsened glucose tolerance.