Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats.

We investigated the effects of ethinyl estradiol (5 mg/kg body wt daily for 5 days, orally) and/or iron sorbitol (50 mg/kg body wt daily for 5 days, i.m.) on bile flow, bile salt independent fraction (BSIF), hepatic delta-aminolevulinate synthase (ALA-S) and uroporphyrinogen decarboxylase (URO-D) in female rats. Ethinyl estradiol administration was associated with a significant decrease of bile flow and BSIF and an increase in URO-D activity in comparison to control values. Iron alone did not modify biliary parameters, but significantly increased the activity of ALA-S. Combined treatment with ethinyl estradiol plus iron partially corrected the reduction of BSIF and restored the activity of ALA-S and URO-D to control levels. Thus iron appears to exert a partially protective effect against ethinyl estradiol-induced cholestasis. No porphyrinogenic effect was observed.

Bile secretion and liver microsomal mixed function oxidase system in mice with griseofulvin-induced hepatic protoporphyria.

Administration of 2.5% griseofulvin in the diet to male CD1 mice produced protoporphyria and cholestasis. Protoporphyria became evident as early as after 10 days of treatment, whereas cholestasis, expressed in terms of total bile flow reduction, developed only after 45 days of griseofulvin. Bile flow impairment was due both to the length of treatment and to the severity of liver protoporphyria. Griseofulvin administration was also associated with a significant modification of the relative amounts of hepatic microsomal cytochromes P-450 and b5, a loss in concentration/mg of protein of cytochrome P-450 and a concomitant increase of b5. Despite these changes, the activity of aniline hydroxylase expressed per mg of microsomal protein, assessed in vitro, was not modified.

Different susceptibility of mouse tissues to porphyrogenic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The porphyrogenic effect of chronic administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (25 micrograms/kg/week) to male C57BL/6 mice was evaluated through quantitative and qualitative analysis of the porphyrins accumulated and of porphyrinogen carboxylase activity in liver, kidney, spleen, brain and erythrocytes. The liver was the principal site of action, both for porphyrin accumulation and for enzyme inhibition, with kidney next, whereas brain and erythrocytes were unaffected. In the spleen, despite unchanged formation of total products of uroporphyrinogen III decarboxylation, both an increase and a decrease of coproporphyrinogen formation were observed, the decrease being concomitant with a higher accumulation of tissue porphyrins. When a response to TCDD was found, the formation of the products of decarboxylaction of uroporphyrinogen III were affected to different extents. The pattern of enzyme inhibition paralleled data reported in the literature regarding tissue distribution of TCDD and indicated that TCDD porphyria is a suitable experimental model for the human 'sporadic' type of porphyria cutanea tarda (PCT).

In vitro inhibitory effect on porphyrinogen carboxylyase of liver extracts from TCDD treated mice.

Marked inhibition of porphyrinogen carboxylyase was produced in vitro by cytosol fractions, deproteinized and free of porphyrins, obtained from livers of mice made porphyric by 9 weeks i.p. treatment with 25 micrograms/kg/week of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Inhibition was proportional to the amount of the fraction added, was increased by preincubation in the absence of the substrate and, once established, could not be reversed by dialysis. TCDD itself, added to the control enzyme in the incubation mixture, did not affect enzyme activity up to a concentration of 77 nM, which is 10 times higher than the liver TCDD concentration found after in vivo TCDD treatment.

Cyclophosphamide-impaired regulation of hepatic heme metabolism.

In male rats hepatic cytochromes b5 and P-450 were reduced at different times after treatment with cyclophosphamide (CP) (200 mg/kg i.p. for 3 days). In contrast, microsomal heme did not change until 48 h after the last dose of CP, leading to accumulation of heme in a 'non-cytochromal' form. Parallel to the above changes the heme metabolism showed derangement: delta-aminolaevulinate synthase, the rate-limiting enzyme in heme synthesis, was depressed and heme oxygenase, the enzyme which catalyzes the oxidative degradation of heme, was increased.

High-performance liquid chromatographic assay of iomeprol in plasma and urine.

A high-performance liquid chromatographic method for assaying the radiographic contrast agent iomeprol in plasma and urine samples is described. Before reversed-phase chromatography, the biological fluids are treated with ion-exchange resins and iopamidol is added as internal standard. The compounds are monitored during elution by ultraviolet-visible spectrometry at 245 nm. The method shows good precision and accuracy and gives similar results to X-ray fluorescence analysis.

Decarboxylation of uroporphyrinogen I and III in 2,3,7,8-tetrachlorodibenzo-p-dioxin induced porphyria in mice.

The decarboxylation of uroporphyrinogens I and III by porphyrinogen carboxy-lyase (EC 4.1.1.37) in mouse liver supernatant was compared in relation to substrate concentrations. In this species uroporphyrinogen III was the best substrate judging by the criteria of Km/Vmax (estimated for total porphyrinogens) and was converted into coproporphyrinogen faster than its series I isomer. The difference between the two isomers was mainly due to the first decarboxylation. This difference was confirmed by calculation of the Hill coefficient and of Lineweaver-Burk plot which suggested that isomer I induced negative cooperativity in the active centre of the enzyme. After treatment with a porphyrogenic dose of TCDD (25 micrograms/kg/week for 9 weeks) differences between uroporphyrinogen I and III as substrate were maintained. In addition treatment reduced Vmax and Km (estimated for total porphyrinogens) of liver porphyrinogen carboxy-lyase to about half control values for both isomers. Vmax was reduced mainly because of the formation of smaller amounts of all products of decarboxylation, and Km because more heptaporphyrinogen was formed than coproporphyrinogen. Values of the Hill coefficient and Lineweaver-Burk plots suggested TCDD induced altered substrate affinity for isomer III too. Treatment with TCDD did not affect the decarboxylation of uroporphyrinogen III by RBC porphyrinogen carboxy-lyase, estimated from Km and Vmax for total porphyrinogens formed.

High-performance liquid chromatographic assay of the magnetic resonance imaging contrast agent gadobenate in plasma, urine and bile.

Gadobenate dimeglumine (Gd-BOPTA-Dimeg) is currently under evaluation as an intravascular paramagnetic contrast agent for magnetic resonance imaging. The anion Gd-BOPTA2- is the moiety of Gd-BOPTA-Dimeg responsible for contrast enhancement. An HPLC method for assaying gadobenate (Gd-BOPTA2-) in plasma, urine and bile samples is described. The analysis is based on the reversed-phase chromatographic separation of the ion pair Gd-BOPTA(2-)-tetrabutylammonium from the endogenous components of biological fluids and its detection by UV absorption at 210 nm. The mean accuracy and precision of the method were in the range -3.4 to +5.0% and 0.2-3.5%, respectively. The method detection limits for Gd-BOPTA2- in plasma (0.8 ml), urine (0.2 ml) and bile (1.0 ml) were 1.1, 7.6 and 1.7 microM (corresponding to 0.73, 5.1 and 1.1 micrograms/ml), respectively.

BeppoSAX and Chandra Observations of SAX J0103.2-7209 = 2E 0101.5-7225: A New Persistent 345 Second X-Ray Pulsar in the Small Magellanic Cloud.

We report the results of a 1998 July BeppoSAX observation of a field in the Small Magellanic Cloud which led to the discovery of approximately 345 s pulsations in the X-ray flux of SAX J0103.2-7209. The BeppoSAX X-ray spectrum is well fitted by an absorbed power law with a photon index of approximately 1.0 plus a blackbody component with kT=0.11 keV. The unabsorbed luminosity in the 2-10 keV energy range is approximately 1.2x1036 ergs s-1. In a very recent Chandra observation, the 345 s pulsations are also detected. The available period measurements provide a constant period derivative of -1.7 s yr-1 over the last 3 years, making SAX J0103.2-7209 one of the most rapidly spinning up X-ray pulsars known. The BeppoSAX position (30&arcsec; uncertainty radius) is consistent with that of the Einstein source 2E 0101.5-7225 and the ROSAT source RX J0103.2-7209. This source was detected at a luminosity level of a few times 1035-1036 ergs s-1 in all data sets of past X-ray missions since 1979. The ROSAT HRI and Chandra positions are consistent with that of a mV=14.8 Be spectral-type star already proposed as the likely optical counterpart of 2E 0101.5-7225. We briefly report and discuss photometric and spectroscopic data carried out at the ESO telescopes 2 days before the BeppoSAX observation. We conclude that SAX J0103.2-7209 and 2E 0101.5-7225 are the same source: a relatively young and persistent X-ray pulsar in the SMC.

Hard X-Ray Emission from the Galaxy Cluster A2256.

After the positive detection by BeppoSAX of hard X-ray radiation up to approximately 80 keV in the Coma Cluster spectrum, we present evidence for nonthermal emission from A2256 in excess of thermal emission at a 4.6 sigma confidence level. In addition to this power-law component, a second nonthermal component already detected by ASCA could be present in the X-ray spectrum of the cluster, which is not surprising given the complex radio morphology of the cluster central region. The spectral index of the hard tail detected by the Phoswich Detection System on board BeppoSAX is marginally consistent with that expected for the inverse Compton model. A value of approximately 0.05 µG is derived for the intracluster magnetic field of the extended radio emission in the northern regions of the cluster, while a higher value of approximately 0.5 µG could be present in the central radio halo, which is likely related to the hard tail detected by ASCA.