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Affinity profiles of morphine, codeine, dihydrocodeine and their glucuronides at opioid receptor subtypes
Life Sciences
|January 1, 1995
Summary
Investigating opioid receptor binding, this study found that chemical changes to morphine, like substitutions or glucuronidation, alter its affinity for mu-, delta-, and kappa-opioid receptors. These modifications independently impact how morphine and its derivatives interact with different receptor subtypes.
Area of Science:
- Pharmacology
- Neuroscience
- Medicinal Chemistry
Background:
- Opioid analgesics like morphine are crucial for pain management.
- Understanding their interaction with specific opioid receptor subtypes (mu, delta, kappa) is key to developing safer and more effective drugs.
- Morphine's chemical structure allows for various modifications, including substitutions and glucuronidation, which can alter its pharmacological profile.
Purpose of the Study:
- To investigate the binding affinities of morphine, codeine, dihydrocodeine, and their glucuronides to mu-, delta-, and kappa-opioid receptors.
- To determine how chemical modifications at the 3- and 6-positions of morphine affect receptor binding.
- To elucidate the impact of glucuronidation on the selectivity of these opioids for different receptor subtypes.
Main Methods:
- Binding assays were performed using guinea-pig brain homogenates.
- Radioligands [3H]DAMGO, [3H]DPDPE, and [3H]U69593 were used to quantify binding to mu-, delta-, and kappa-opioid receptors, respectively.
- The affinities of morphine, codeine, dihydrocodeine, and their glucuronides were measured.
Main Results:
- Substitution of morphine's free phenolic group decreased overall opioid receptor binding.
- Glucuronidation of the 6-hydroxyl group did not alter mu-receptor affinity but slightly increased delta-receptor affinity and reduced kappa-receptor affinity.
- The 6-glucuronides showed decreased selectivity for mu-receptors over delta-receptors and increased selectivity for mu-receptors over kappa-receptors.
Conclusions:
- Chemical modifications at the 3- and 6-positions of morphine independently influence its affinity for opioid receptor subtypes.
- Glucuronidation at the 6-position significantly alters the receptor binding profile, impacting selectivity.
- These findings provide insights into structure-activity relationships for opioid analgesics and can guide the design of novel opioid-based therapeutics.