[Production of morphinone as a metabolite of morphine and its physiological role]

Opioids and Vitamin C: Known Interactions and Potential for Redox-Signaling Crosstalk

Opioids are among the most widely used classes of pharmacologically active compounds both clinically and recreationally. Beyond their analgesic efficacy via μ opioid receptor (MOR) agonism, a prominent side effect is central respiratory depression, leading to systemic hypoxia and free radical generation. Vitamin C (ascorbic acid; AA) is an essential antioxidant vitamin and is involved in the recycling of redox cofactors associated with inflammation. While AA has been shown to reduce some of the negative side effects of opioids, the underlying mechanisms have not been explored. The present review seeks to provide a signaling framework under which MOR activation and AA may interact. AA can directly quench reactive oxygen and nitrogen species induced by opioids, yet this activity alone does not sufficiently describe observations. Downstream of MOR activation, confounding effects from AA with STAT3, HIF1α, and NF-κB have the potential to block production of antioxidant proteins such as nitric oxide synthase and superoxide dismutase. Further mechanistic research is necessary to understand the underlying signaling crosstalk of MOR activation and AA in the amelioration of the negative, potentially fatal side effects of opioids.

Morphine dependence is attenuated by red ginseng extract and ginsenosides Rh2, Rg3, and compound K

BACKGROUND

Red ginseng and ginsenosides have shown plethoric effects against various ailments. However, little is known regarding the effect of red ginseng on morphine-induced dependence and tolerance. We therefore investigated the effect of red ginseng extract (RGE) and biotransformed ginsenosides Rh2, Rg3, and compound K on morphine-induced dependence in mice and rats.

METHODS

While mice were pretreated with RGE and then morphine was injected intraperitoneally, rats were infused with ginsenosides and morphine intracranially for 7 days. Naloxone-induced morphine withdrawal syndrome was estimated and conditioned place preference test was performed for physical and psychological dependence, respectively. Western blotting was used to measure protein expressions.

RESULTS

Whereas RGE inhibited the number of naloxone-precipitated jumps and reduced conditioned place preference score, it restored the level of glutathione in mice. Likewise, ginsenosides Rh2, Rg3, and compound K attenuated morphine-dependent behavioral patterns such as teeth chattering, grooming, wet-dog shake, and escape behavior in rats. Moreover, activated N-methyl-D-aspartate acid receptor subunit 1 and extracellular signal-regulated kinase in the frontal cortex of rats, and cultured cortical neurons from mice were downregulated by ginsenosides Rh2, Rg3, and compound K despite their differential effects.

CONCLUSION

RGE and biotransformed ginsenosides could be considered as potential therapeutic agents against morphine-induced dependence.

Bergenin decreases the morphine-induced physical dependence via antioxidative activity in mice

Oxidative stress plays a role in the development of physical dependence induced by morphine. Bergenin, a polyphenol found in many Asian, African, and South American medicinal plants, is a potent antinarcotic agent with wide spectrum of pharmacological activities including antioxidant action. In the present study, we observed that bergenin decreased the development of physical dependence induced by morphine in mice and the antioxidant activity of bergenin plays a role in the antinarcotic effects through adapting to morphine-induced oxidative stress in the brain. The naloxone-precipitated withdrawal symptom (jumping frequency) was significantly ameliorated (50% of control group) by administration of bergenin (20 mg/kg) in morphine-treated mice. Furthermore, morphine-induced down-regulation of glutathione (GSH) contents was reversed by bergenin administration in the frontal cortex and liver. Bergenin had no effects on the increased levels of nfr2-dependent antioxidant enzyme HO1 and NQO1 in the frontal cortex, striatum, and liver of morphine-treated mice. However, the morphine-induced increase in nrf2 nuclear translocation in the frontal cortex and striatum was inhibited by bergenin treatment. These results suggest that bergenin has a potential antinarcotic effect via regulation of GSH contents and oxidative stress.

Can you vaccinate against substance abuse?

Vaccines are being developed against substance abuse and most progress has been made with anti-cocaine, nicotine and opiate vaccines, but new ones are being developed for methamphetamine and may be in humans within 18 - 24 months. These haptenated vaccines share a common problem in that only about one-third of those vaccinated get a sufficiently robust antibody titer to enable them to effectively block drug use. This problem is being addressed with better carrier proteins and new adjuvants beyond alum. This review provides details about these developing vaccines that act through pharmacokinetic rather than pharmacodynamics blockade. Due to this pharmacokinetic mechanism of keeping abused drugs in the bloodstream and not allowing them entry into the brain or other organs, these vaccines have very few side effects compared to other blockers used in addictions treatment.

Characterization of rabbit morphine 6-dehydrogenase and two NAD(+)-dependent 3α(17β)-hydroxysteroid dehydrogenases

Mammalian morphine 6-dehydrogenase (M6DH)(1) converts morphine into a reactive electrophile, morphinone. M6DH belongs to the aldo-keto reductase (AKR) superfamily, but its endogenous substrates and entire amino acid sequence remain unknown. A recent rabbit genomic sequencing predicts three genes for novel AKRs (1C26, 1C27 and 1C28) that share >87% amino acid sequence identity and are similar to the partial sequence of rabbit liver M6DH. We isolated cDNAs for the three AKRs, and compared the properties of their recombinant enzymes. Like M6DH, only AKR1C26 that shares the highest sequence identity with hepatic M6DH oxidized morphine. The three AKRs showed NAD(+)-dependent dehydrogenase activity towards other non-steroidal alicyclic alcohols and 3α/17β-hydroxy-C(18)/C(19)/C(21)-steroids, and their mRNAs were ubiquitously expressed in rabbit tissues. The kinetic constants for the substrates suggest that at least AKR1C26 and AKR1C28 act as NAD(+)-dependent 3α/17β-hydroxysteroid dehydrogenases. AKR1C27 differed from AKR1C28 in its high K(m) values for the substrates and low sensitivity towards competitive inhibitors (ikarisoside A, hinokitiol, hexestrol and zearalenone), despite their 95% sequence identity. The site-directed mutagenesis of Tyr118 and Phe310 in AKR1C27 to the corresponding residues (Phe and Ile, respectively) in AKR1C28 produced an enzyme that was similar to AKR1C28, suggesting their key roles in ligand binding.

Multiplicity of mammalian reductases for xenobiotic carbonyl compounds

A variety of carbonyl compounds are present in foods, environmental pollutants, and drugs. These xenobiotic carbonyl compounds are metabolized into the corresponding alcohols by many mammalian NAD(P)H-dependent reductases, which belong to the short-chain dehydrogenase/reductase (SDR) and aldo-keto reductase superfamilies. Recent genomic analysis, cDNA isolation and characterization of the recombinant enzymes suggested that, in humans, the six members of each of the two superfamilies, i.e., total of 12 enzymes, are involved in the reductive metabolism of xenobiotic carbonyl compounds. They comprise three types of carbonyl reductase, dehydrogenase/reductase (SDR family) member 4, 11beta-hydroxysteroid dehydrogenase type 1, L-xylulose reductase, two types of aflatoxin B1 aldehyde reductase, 20alpha-hydroxysteroid dehydrogenase, and three types of 3alpha-hydroxysteroid dehydrogenase. Accumulating data on the human enzymes provide new insights into their roles in cellular and molecular reactions including xenobiotic metabolism. On the other hand, mice and rats lack the gene for a protein corresponding to human 3alpha-hydroxysteroid dehydrogenase type 3, but instead possess additional five or six genes encoding proteins that are structurally related to human hydroxysteroid dehydrogenases. Characterization of the additional enzymes suggested their involvement in species-specific biological events and species differences in the metabolism of xenobiotic carbonyl compounds.

Characterization of Two Isoforms of Mouse 3(17).ALPHA.-Hydroxysteroid Dehydrogenases of the Aldo-Keto Reductase Family

Mouse kidney contains two 3(17)alpha-hydroxysteroid dehydrogenases (HSDs) that show essentially the same properties except for their isoelectric points. However, the structural differences and physiological roles of the two enzymes remain unknown. In this study, we have isolated cDNAs for the two 3(17)alpha-HSDs from a total RNA sample of mouse kidney by reverse transcription-PCR. The identity of the cDNAs was confirmed by characterization of the recombinant enzymes that showed the same molecular weights, pI values, pH optima, substrate specificity and inhibitor sensitivity as those of the enzymes from mouse kidney. We also found that the recombinant enzymes reduce precursors of neuroactive progesterone derivatives, 5alpha-dihydrotestoserone, deoxycorticosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate and estrone at low Km values of 0.3-2 microM. The two enzymes belonged to the aldo-keto reductase (AKR) family, and their 323-amino acid sequences differed only by five amino acids. The sequences of the two isoforms are identical to those of proteins that are predicted to be encoded in a gene for AKR1C21 in the database of the mouse genome. However, the mRNAs for the two isoforms were expressed in mouse kidney and other tissues, in which their expression levels were different. The results indicate an important role of 3(17)alpha-HSD in controlling the concentrations of various steroid hormones in the mouse tissues, and suggest the existence of two genes for the two isoforms of the enzyme.