Genetic susceptibility to substance dependence.

Despite what is often believed, the majority of those who experiment with substances with a dependence potential do not develop dependence. However, there is a subpopulation of users that easily becomes dependent on substances, and these individuals exhibit pre-existing comorbid traits, including novelty seeking and antisocial behavior. There appears to be a genetic basis for the susceptibility to dependence and these comorbid traits. Animal studies have identified specific genes that can alter susceptibility to dependence and response to novelty. The mechanisms underlying the genetic susceptibility to dependence and response to novelty are complex, but genetic susceptibility plays a significant role in the transition from substance use to dependence and from chronic use to addiction. We discuss two models to explain how genetic variations alter dependence susceptibility. Identification of the specific genes involved in these processes would help to identify individuals that are vulnerable to dependence/addiction and to devise novel treatment strategies.

Indoxyl-beta-D-glucuronide and 3-indoxyl sulfate in plasma of hemodialysis patients.

The content of indoxyl-beta-D-glucuronide, which has been found in patients' plasma as a new indicator of renal failure, logarithmically correlated with that of 3-indoxyl sulfate (indican) in the plasma of hemodialysis patients, showing another weak correlation with beta(2)-microglobulin content. The content ratio of indoxyl-beta-D-glucuronide to 3-indoxyl sulfate (IG/IS) gradually increased depending on the duration of hemodialysis treatment. Indoxyl-beta-D-glucuronide could be easily dialyzed in the hemodialysis treatment, in contrast to hardly dialyzable 3-indoxyl sulfate which bound to plasma proteins. Therefore, glucuronide conjugation in indole excretion is favorable for hemodialysis patients in that it eliminates indoxyl compounds in blood by hemodialysis.

Indoxyl-beta-D-glucuronide, the primary emitter of low-level chemiluminescence in plasma of hemodialysis patients.

Characteristic light emission induced by the oxidation of hydroxyl radicals has been found in plasma of hemodialysis patients (Agatsuma et al., Clin Chem 1992;38:48-55). We purified a primary emitter, a chemiluminescent component peaking at 430 nm, by anion-exchange chromatography and reversed-phase HPLC. By using proton nuclear magnetic resonance and authentic indoxyl compounds, we determined the primary emitter to be indoxyl-beta-D-glucuronide. Absorption and fluorescence spectra of the purified sample coincided well with those of authentic indoxyl-beta-D-glucuronide, as did the peak in the chemiluminescence emission spectrum. Retention time of the purified sample on reversed-phase HPLC, measured by fluorescence, was also in accordance with that of indoxyl-beta-D-glucuronide. To our knowledge, this is the first identification of a primary emitter of low-level chemiluminescence from a biological source.

Hydroxyl radical-induced characteristic chemiluminescent spectra from plasma of hemodialysis patients.

Plasma from hemodialysis patients evoked weak photon emissions (chemiluminescence) in a characteristic emission spectrum with a peak at 430 nm, attributed to attack by hydroxyl radicals generated from the iron-catalyzed breakdown of hydrogen peroxide (Fenton reaction), whereas plasma from normal healthy subjects showed a rather weak red chemiluminescence peak at around 680 nm, similar to that resulting from attack by hydroxyl radicals. However, the addition of hydrogen peroxide in the absence of divalent irons induced almost the same red chemiluminescent emission spectrum in both plasmas. The HPLC-gel-filtration chromatography carried out with both plasmas revealed that a primary emitter evoking a peak emission at 430 nm was located in the fraction of lower-molecular-mass substances in fractionated plasma from hemodialysis patients. In contrast, the elution peaks evoking red chemiluminescence with the addition of hydrogen peroxide were mainly observed for the higher-molecular-mass fraction, as determined by gel chromatography of both plasmas. Therefore, the observation of a chemiluminescence peak at 430 nm, induced by the generation of hydroxyl radicals, correlated well with chemiluminescent emissions in plasma samples from patients with chronic renal failure. Spectral analyses of clinical samples that show weak chemiluminescence by forced oxidation by such an active oxygen may provide a new and more sensitive method for diagnosing metabolic disorders.

Weak chemiluminescence of bilirubin and its stimulation by aldehydes.

Bilirubin in an alkaline solution exhibits a weak chemiluminescence (CL) under aerobic conditions. This spontaneous CL was markedly enhanced by the addition of various aldehydes. The fluorescent emission spectrum of bilirubin, excited by weak intensity light at 350 nm, coincided with its CL emission spectrum (peak at 670 nm). CL emission from bilirubin was not quenched by active oxygen scavengers. This suggests that triplet oxygen reacts with bilirubin, and forms an oxygenated intermediate (hydroperoxide) as a primary emitter (oxidative scission of tetrapyrrole bonds in bilirubin is not involved in this CL). The Ehrlich reaction (test for monopyrroles) and hydrolsulphite reaction (test for dipyrroles) on the CL reaction mixture and unreacted bilirubin showed no differences. When the CL was initiated by singlet oxygen, rather than superoxide anion, monopyrrole, was detected in the reaction products by gel chromatography. The inhibitory effect of a scavenger of singlet oxygen on CL was eliminated in the presence of formaldehyde. Therefore, triplet carbonyl, formed by singlet oxygen through the dioxetane structure in bilirubin, is not an emitter. The reaction mechanism of bilirubin CL and the formation of a hydroperoxide intermediate is discussed in relation to the chemical structure of luciferin molecules from bioluminescent organisms.

Bilirubin chemiluminescence induced by the attack of active oxygen species.

Ultraweak chemiluminescence (CL) from bilirubin occurs in the presence of triplet oxygen and is stimulated by the addition of aldehydes. Active oxygen species also enhance bilirubin CL, in the absence of aldehydes. An inhibitory effect of active oxygen scavengers on the CL indicated that active oxygens generated from the decomposition of added hydrogen peroxide or from the xanthine-xanthine oxidase reaction contributed to the CL from bilirubin molecules. However, the contribution of singlet oxygen to the CL disappeared in the presence of formaldehyde. This suggested that the scission of tetrapyrrole bonds via a dioxetane intermediate or the production of triplet carbonyls from the oxidation of aldehydes by singlet oxygen was not involved in the CL, at least in the presence of formaldehyde. The spectrum of CL induced by the generation of active oxygen was the same as that from the aldehyde-enhanced CL reaction. We propose that the formation of a hydroperoxide (and/or hydroxide) bilirubin intermediate, but not a dioxetane, may be involved in the excitation of bilirubin molecules for CL.