Melatonin modulates drug-induced acute porphyria.

This work investigated the modulation by melatonin (Mel) of the effects of the porphyrinogenic drugs 2-allyl-2-isopropylacetamide (AIA) and 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-collidine (DDC) on oxidative environment, glucose biosynthesis and heme pathway parameters. Administration of Mel before rat intoxication with AIA/DDC showed a clear beneficial effect in all cases. Mel induced decreases of 42% and 35% in the excretion of the hemeprecursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG), respectively, and a 33% decrease in the induction of the heme regulatory enzyme 5-aminolevulinic acid-synthase (ALA-S). The activity of the glucose metabolism enzyme phosphoenolpyruvate carboxykinase (PEPCK), which had been diminished by the porphyrinogenic treatment, was restored by 45% when animals were pre-treated with Mel. Mel abolished the modest decrease in glucose 6-phospatase (G6Pase) activity caused by AIA/DDC treatment. The oxidative status of lipids was attenuated by Mel treatment in homogenates by 47%, whereas no statistically significant AIA/DDC-induced increase in thiobarbituric acid reactive substances (TBARS) was observed in microsomes after Mel pre-treatment. We hypothesize that Mel may be scavenging reactive species of oxygen (ROS) that could be damaging lipids, PEPCK, G6Pase and ferrochelatase (FQ). Additionally, Mel administration resulted in the repression of the key enzyme ALA-S, and this could be due to an increase in glucose levels, which is known to inhibit ALA-S induction. The consequent decrease in levels of the heme precursors ALA and PBG had a beneficial effect on the drug-induced porphyria. The results obtained open the possibility of further research on the use of melatonin as a co-treatment option in acute porphyria.

Hepatic alteration of tryptophan metabolism in an acute porphyria model Its relation with gluconeogenic blockage.

This study focuses on the alterations suffered by the serotoninergic and kinurenergic routes of tryptophan (TRP) metabolism in liver, and their relation with gluconeogenic phosphoenolpyruvate-carboxykinase (PEPCK) blockage in experimental acute porphyria. This porphyria was induced in rats by a combined treatment of 2-allyl-2-isopropylacetamide (100, 250, 500 mg/kg bw) and 3,5-dietoxicarbonil 1,4-dihydrocollidine (constant 50 mg/kg bw dose). Results showed a marked dose-dependent increase of all TRP pyrrolase (TRPp) forms, active (holo, total) and inactive (apo), and a decrease in the degree of enzyme saturation by heme. Increases for holo, total, and apo-TRPp were 90, 150, and 230%, respectively, at the highest dose assayed (H). The treatment also impaired the serotoninergic route of TRP metabolism in liver, causing a decrease in serotonin level (H, 38%), and a concomitant enhancement in TRP content (H, 23%). The porphyrinogenic treatment promoted a blockage in PEPCK activity (H, 30%). This occurred in correlation to the development of porphyria, to TRPp alterations and to the production of hepatic microsomal thiobarbituric acid reactive substances. Porphyria was estimated through increases in 5-aminolevulinic acid-synthase (ALA-S) activity, ALA and porphobilinogen contents, and a decrease in ferrochelatase activity. Thus, the TRP kynurenine route was augmented whereas the serotoninergic route was reduced. PEPCK blockage could be partly attributed to quinolinate generated from TRP by the increase of TRPp activity, which would be due to the effect of porphyrinogenic drugs on TRP. The contribution of ROS to PEPCK blockage is analyzed. Likewise, the implication of these results in the control of porphyrias by glucose is discussed.

Melatonin formation in pineal gland from rats with hexachlorobenzene experimental porphyria.

Hexachlorobenzene produces an experimental hepatic porphyria in rats, which is similar to human porphyria cutanea tarda, with hyperpigmentation as one of its characteristic features. Alterations in tryptophan metabolism have been previously observed in this chronic porphyria. Melatonin formation from tryptophan via serotonin shows diurnal rhythmicity in the pineal gland, and higher values are observed during the dark phase of an imposed light-dark cycle. The purpose of this study was to determine the contents of tryptophan and its metabolites in pineal gland of normal and hexachlorobenzene-treated rats in order to find alterations potentially related to porphyria cutanea tarda. Results show that in animals with this experimental porphyria some tryptophan metabolite levels (serotonin and 5-hydroxyindoleacetic acid) increase only during the light period, whereas tryptophan content remained equal to the controls. Hydroxyindole-O-methyltransferase activity also increases by light in pineal gland from hexachlorobenzene-treated rats. On the other hand, tryptophan is converted to melatonin in the dark period, but this route is not exacerbated in hexachlorobenzene porphyria. The relevance of these alterations is discussed in relation to hyperpigmentation, neoplastic and oxidative stress processes associated with this porphyria.

Hexachlorobenzene as hormonal disruptor--studies about glucocorticoids: their hepatic receptors, adrenal synthesis and plasma levels in relation to impaired gluconeogenesis.

In Wistar rats, hexachlorobenzene (HCB) depresses the gluconeogenic enzyme phosphoenolpyruvate-carboxykinase (PEPCK). In the liver, glucocorticoids (GC) normally regulate the glucose synthesis by acting on PEPCK. Thus, the aim of this work was to investigate, in a time-course study, the effects of HCB on plasma GC, its adrenal synthesis and stimulation, and the kinetic parameters of its hepatic receptors (GR) in relation to the gluconeogenic blockage produced by HCB. Plasma corticosterone (CORT) concentration, urinary porphyrins and hepatic PEPCK were determined after 2, 4, 6 and 8 weeks of HCB-treatment. The effect of HCB on kinetic parameters of GR was studied in adrenalectomized porphyric rats after 2, 4 and 8 weeks of treatment. Additionally, adrenal CORT synthesis in the same weeks was measured with or without ACTH. Results show that plasma CORT in intoxicated animals dropped significantly after 2 and 4 weeks of treatment (23% and 58%, respectively), and then remained constant until the 8th week. HCB also promoted a reduction in the number of hepatic GR (50-55%) without modifying affinity. After 8 weeks, when porphyria was well established (40-50-fold increase in urinary porphyrins), a reduction (52%) in hepatic GR number, as well as a decrease in PEPCK activity (56%) were observed. Moreover, CORT biosynthesis in adrenals from intoxicated animals significantly decreased (60%) without changes in ACTH effect. Briefly, this paper shows that HCB causes a disruption in GC and GR. This disturbance could contribute to the negative effect on glucose synthesis through PEPCK regulation, thus modulating porphyria. These results enhance the knowledge about the hormonal disruption produced by chlorinated xenobiotics.

Response of glucose metabolism enzymes in an acute porphyria model. Role of reactive oxygen species.

Acute hepatic porphyrias are human metabolic diseases characterized by the accumulation of heme precursors, such as 5-aminolevulinic acid (ALA). The administration of glucose can prevent the symptomatology of these diseases. The aim of this work was to study the relationship between glucose metabolism disturbances and the development of experimental acute hepatic porphyria, as well as the role of reactive oxygen species (ROS) through assays on hepatic key gluconeogenic and glycogenolytic enzymes; phosphoenolpyruvate carboxykinase (PEPCK) and glycogen phosphorylase (GP), respectively. Female Wistar rats were treated with three different doses of the porphyrinogenic drug 2-allyl-2-isopropylacetamide (AIA) and with a single dose of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Thus, rats were divided into the following groups: group L (100 mg AIA + 50 mg DDC/kg body wt.); group M (250 mg AIA + 50 mg DDC/kg body wt.) and group H (500 mg AIA + 50 mg DDC/kg body wt.). The control group (group C) only received vehicles (saline solution and corn oil). Acute hepatic porphyria markers ALA-synthase (ALA-S) and ferrochelatase, heme precursors ALA and porphobilinogen (PBG), and oxidative stress markers superoxide dismutase (SOD) and catalase (CAT) were also measured in hepatic tissue. On the other hand, hepatic cytosolic protein carbonyl content, lipid peroxidation and urinary chemiluminescence were determined as in vivo oxidative damage markers. All these parameters were studied in relation to the different doses of AIA/DDC. Results showed that enzymes were affected in a drug-dose-dependent way. PEPCK activity decreased about 30% in group H with respect to groups C and L, whereas GP activity decreased 53 and 38% in group H when compared to groups C and L, respectively. On the other hand, cytosolic protein carbonyl content increased three-fold in group H with respect to group C. A marked increase in urinary chemiluminescence and a definite increase in lipid peroxidation were also detected. The activity of liver antioxidant enzyme SOD showed an induction of about 235% in group H when compared to group C, whereas CAT activity diminished due to heme depletion caused by both drugs. Based on these results, we can speculate that the alterations observed in glucose metabolism enzymes could be partly related to the damage caused by ROS on their enzymatic protein structures, suggesting that they could be also linked to the beneficial role of glucose administration in acute hepatic porphyria cases.