Physico-chemical characterization of bilirubin-10-sulfonate and comparison of its acid-base behavior with unconjugated bilirubin.

Unconjugated bilirubin (UCB) is the end-product of heme catabolism in the intravascular compartment. Although beneficial for human health when mildly elevated in the body, when present at greater than a critical threshold concentration, UCB exerts toxic effects that are related to its physico-chemical properties, particularly affecting the central nervous system. The aim of the present study was to characterize bilirubin-10-sulfonate (ranarubin), a naturally occurring bile pigment, including determination of its mixed acidity constants (pKa*). Thanks to the presence of the sulfonic acid moiety, this compound is more polar compared to UCB, which might theoretically solve the problem with an accurate determination of the UCB pKa* values of its propionic acid carboxylic groups. Bilirubin-10-sulfonate was synthesized by modification of a previously described procedure; and its properties were studied by mass spectrometry (MS), nuclear magnetic resonance (NMR), infrared (IR), and circular dichroism (CD) spectroscopy. Determination of pKa* values of bilirubin-10-sulfonate and UCB was performed by capillary electrophoresis with low pigment concentrations in polar buffers. The identity of the synthesized bilirubin-10-sulfonate was confirmed by MS, and the pigment was further characterized by NMR, IR, and CD spectroscopy. The pKa values of carboxylic acid moieties of bilirubin-10-sulfonate were determined to be 5.02, whereas those of UCB were determined to be 9.01. The physico-chemical properties of bilirubin-10-sulfonate were partially characterized with low pKa* values compared to those of UCB, indicating that bilirubin-10-sulfonate cannot be used as a surrogate pigment for UCB chemical studies. In addition, using a different methodological approach, the pKa* values of UCB were found to be in a mildly alkaline region, confirming the conclusions of a recent critical re-evaluation of this specific issue.

Reduction of bilirubin ditaurate by the intestinal bacterium Clostridium perfringens.

Bilirubin is degraded in the human gut by microflora into urobilinoids. In our study we investigated whether the bilirubin-reducing strain of Clostridium perfringens can reduce bilirubin ditaurate (BDT), a bile pigment of some lower vertebrates, without hydrolysis of the taurine moiety. C. perfringes was incubated under anaerobic conditions with BDT; reduction products were quantified by spectrophotometry and separated by TLC. Based on Rf values of BDT reduction products and synthetic urobilinogen ditaurate, three novel taurine-conjugated urobilinoids were identified. It is likely that bilirubin-reducing enzyme(s) serve for the effective disposal of electrons produced by fermentolytic processes in these anaerobic bacteria.

Trace elements status in selenium-deficient rats--interaction with cadmium.

Although the metabolic and toxicological interactions between essential element selenium (Se) and toxic element cadmium (Cd) have been reported for a long time, the experimental studies explored mostly acute, high-dose interactions. Limited data are available regarding the effects of Se-deficiency on toxicokinetics of cadmium, as well as on the levels of key trace elements--copper, zinc, and iron. In the present study, male and female Wistar weanling rats (n = 40/41) were fed either Se-deficient or Se-adequate diet (<0.06 or 0.14 mg Se per kilogram diet, respectively) for 12 weeks, and from week 9 were drinking water containing 0 or 50 mg Cd/l as cadmium chloride. At the end of the 12-week period, trace element concentrations were estimated by AAS. Selenium-deficient rats of both genders showed significantly lower accumulation of cadmium in the liver, compared to Se-adequate rats. Zinc and iron hepatic levels were not affected by Se-deficiency. However, a significant elevation of copper was found in the liver of Se-deficient rats of both genders. Cadmium supplementation increased zinc and decreased iron hepatic level, regardless of Se status and decreased copper concentration in Se-adequate rats. Se-deficiency was also found to influence the effectiveness of cadmium mobilization in male rats.

The influence of curcumin and manganese complex of curcumin on cadmium-induced oxidative damage and trace elements status in tissues of mice.

Curcumin (diferuoyl methane) from turmeric is a well-known biologically active compound. It has been shown to ameliorate oxidative stress and it is considered to be a potent cancer chemopreventive agent. In our previous study the antioxidative effects of curcumin in cadmium exposed animals were demonstrated. Also manganese exerts protective effects in experimental cadmium intoxication. The present study examined the ability of the manganese complex of curcumin (Mn-curcumin) and curcumin to protect against oxidative damage and changes in trace element status in cadmium-intoxicated male mice. Curcumin or Mn-curcumin were administered at equimolar doses (0.14 mmol/kg b.w.) for 3 days, by gastric gavages, dispersed in methylcellulose. One hour after the last dose of antioxidants, cadmium chloride (33 micromol/kg) was administered subcutaneously. Both curcumin and Mn-curcumin prevented the increase of hepatic lipid peroxidation -- expressed as MDA level, induced by cadmium intoxication and attenuated the Cd-induced decrease of hepatic GSH level. No change in hepatic glutathione peroxidase or catalase activities was found in Cd-exposed mice. A decreased GSH-Px activity was measured in curcumin and Mn-curcumin alone treated mice. Neither curcumin nor Mn-curcumin treatment influenced cadmium distribution in the tissues and did not correct the changes in the balance of essential elements caused by Cd-treatment. The treatment with Mn-curcumin increased the Fe and Mn content in the kidneys of both control and Cd-treated mice and Fe and Cu content in the brain of control mice. In conclusion, regarding the antioxidative action, introducing manganese into the curcumin molecule does not potentiate the studied effects of curcumin.