Changing M3G/M6G ratios and pharmacodynamics in a cancer patient during long-term morphine treatment

Morphine-3-Glucuronide, Physiology and Behavior

Morphine remains the gold standard painkiller available to date to relieve severe pain. Morphine metabolism leads to the production of two predominant metabolites, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). This metabolism involves uridine 5′-diphospho-glucuronosyltransferases (UGTs), which catalyze the addition of a glucuronide moiety onto the C3 or C6 position of morphine. Interestingly, M3G and M6G have been shown to be biologically active. On the one hand, M6G produces potent analgesia in rodents and humans. On the other hand, M3G provokes a state of strong excitation in rodents, characterized by thermal hyperalgesia and tactile allodynia. Its coadministration with morphine or M6G also reduces the resulting analgesia. Although these behavioral effects show quite consistency in rodents, M3G effects are much more debated in humans and the identity of the receptor(s) on which M3G acts remains unclear. Indeed, M3G has little affinity for mu opioid receptor (MOR) (on which morphine binds) and its effects are retained in the presence of naloxone or naltrexone, two non-selective MOR antagonists. Paradoxically, MOR seems to be essential to M3G effects. In contrast, several studies proposed that TLR4 could mediate M3G effects since this receptor also appears to be essential to M3G-induced hyperalgesia. This review summarizes M3G’s behavioral effects and potential targets in the central nervous system, as well as the mechanisms by which it might oppose analgesia.

Morphine-3-glucuronide upregulates PD-L1 expression via TLR4 and promotes the immune escape of non-small cell lung cancer

Objective

Patients with cancer pain are highly dependent on morphine analgesia, but studies have shown a negative correlation between morphine demand and patient outcomes. The long-term use of morphine may result in abnormally elevated serum morphine-3-glucuronide (M3G) levels. Hence, the effects of M3G on tumor progression are worth studying.

Methods

The effects of M3G on PD-L1 expressions in human non-small cell lung cancer (NSCLC) cell lines were first evaluated. Activation of TLR4 downstream pathways after M3G treatment was then determined by Western blot. The effects of M3G on human cytotoxic T lymphocytes (CTL) cytotoxicity and INF-γ release was also detected. Finally, the LLC murine lung adenocarcinoma cell line were used to establish a murine lung cancer model, and the effects of M3G on tumor growth and metastasis were determined.

Results

M3G promoted the expressions of PD-L1 in the A549 and H1299 cell lines in a TLR4-dependent manner (P < 0.05). M3G activated the PI3K and the NFκB signaling pathways, and this effect was antagonized by a TLR4 pathway inhibitor. A PI3K pathway inhibitor reversed the M3G-mediated PD-L1 upregulation. M3G inhibited the cytotoxicity of CTL on A549 cells and decreased the level of INF-γ. Repeated M3G intraperitoneal injections promoted LLC tumor growth and lung metastasis through the upregulation of tumor expressed PD-L1 and the reduction of CTL in the tumor microenvironment.

Conclusions

M3G specifically activated TLR4 in NSCLC cells and upregulated PD-L1 expression through the PI3K signaling pathway, thereby inhibiting CTL cytotoxicity and finally promoting tumor immune escape.

Transdermal opioid patches for pain treatment in ancient Greece

Pain treatment in ancient Greece, and through the middle ages in Europe, was to a great extent based on the expertise of the Greek physician Galen (c. 129-200 A.D.). Galen makes particular reference to "Olympic Victor's Dark Ointment" (OVDO), which is listed with a number of collyria. Galen states that OVDO can be useful for treating extreme pain and swellings, forming one of the best eye salves. Olympic Victor's Dark Ointment, an opium-based treatment, forms a "patch" when applied externally as an ointment, because it quickly dries to cover a localized region but still retains its elastic properties. This study has recreated OVDO and applied the ointment to abdominal mouse skin, in vitro. To assess the efficacy of OVDO, the transdermal transfer of morphine was measured when given as OVDO and compared to morphine administered in the form of a solution of Opium + PBS (ringer). Olympic Victor's Dark Ointment showed a transdermal transfer of morphine over time comparable to 25% of the most efficient modern transdermal opioid patches, while hardly any morphine was able to penetrate the skin when applied mixed in PBS. We conclude that OVDO is very efficient in its composition and may carry some forgotten abilities in terms of drug delivery, which could be transferred to modern medicine. Indeed, this may lead to a better choice of morphine use and controlled management in individual patient cases, taking both pain relief and anti-inflammatory aspects into account.

Improved practices for safe administration of intravenous bolus morphine in a pediatric setting

Postoperative pain control is a clinical imperative, for which morphine is a preferred opioid. However, interpatient variability and drug accumulation with repeated doses, as well as medication errors, may result in respiratory arrest with this medication. Early detection of respiratory depression is essential for safe use of morphine, following both initial and repeated doses. A multidisciplinary team contributed to development of an intravenous (IV) bolus morphine monitoring guideline that reflects current knowledge of morphine pharmacokinetics. Monitoring over a 22-week period in a postsurgical unit was then assessed via record review. A total of 270 postsurgical patients received a first dose of IV bolus morphine, with 784 subsequent doses also administered. Complete monitoring (heart rate, respiratory rate, blood pressure, sedation score, oxygen saturation, and pain score) after the morphine bolus was documented at baseline and 10 and 20 minutes for 34%, 30%, and 23%, respectively, of the patients; partial monitoring (respiratory rate and oxygen saturation) was documented for an additional 22%, 15%, and 9% of patients; 43% of subsequent morphine doses were followed with complete monitoring, and an additional 30% with at least partial monitoring. Adherence to the monitoring procedure fluctuated over the study period with no consistent upward or downward trend. A small number of children exhibited a reduced respiratory rate potentially indicating respiratory depression, but no child required antidote or respiratory support. Despite suboptimal guideline adherence, potential signs of respiratory depression were detected that might otherwise have gone unnoticed. This validates the improved guideline and suggests that some incidents may have remained undetected. Front-line staff must be involved to optimize change, champion the initiative, and promote patient safety.

[Do opioids induce hyperalgesia?]

Opioids are the most potent drugs for treatment of acute and chronic pain. However, accumulating evidence suggests that opioids may paradoxically also enhance pain, often referred to as opioid-induced hyperalgesia. Opioid-induced hyperalgesia is defined as an increased sensitivity to pain or a decreased pain threshold in response to opioid therapy. Several mechanisms have been proposed to support opioid-induced hyperalgesia. However, it remains unclear whether opioid-induced hyperalgesia develops during continuous chronic application of opioids or on their withdrawal. This review provides a comprehensive summary of clinical research concerning opioid-induced hyperalgesia and the molecular mechanisms of opioid withdrawal and opioid tolerance and other potential mechanisms which might induce hyperalgesia during opioid therapy will be discussed. The status quo of our knowledge will be summarized and the clinical relevance of opioid-induced hyperalgesia will be discussed.

High levels of morphine-6-glucuronide in street heroin addicts

RATIONALE

In the body, heroin is rapidly transformed to 6-acetylmorphine (6-AM) and then to morphine, that in turn is mainly metabolized to morphine-3-glucuronide (M3G) and, at lesser extent, to morphine-6-glucuronide (M6G). Unlike M3G, M6G is a potent opioid agonist. Intravenous heroin abusers (IHU) are exposed to a wide array of drugs and contaminants that might affect glucuronidation.

OBJECTIVES

We assessed plasma and urine concentrations of M3G and M6G in four groups of subjects: the first two included long-term IHU either exposed to street heroin ( n=8) or receiving a single IV injection of morphine ( n=4), while the other two groups included non-IHU patients receiving acute IV ( n=8) or chronic oral ( n=6) administrations of morphine.

METHODS

After solid phase extraction plasma and urine concentrations of morphine metabolites were determined by HPLC analyses.

RESULTS

M3G accounted for the greater part of morphine glucuronides detected in body fluids of non-IHU patients treated with morphine. This pattern of metabolism remained stable across 15 days of oral administration of incremental doses of morphine. In contrast, the two groups of IHU (street heroin taking or morphine-treated subjects) showed a reduction of blood and urine M3G concentrations in favor of M6G. Consequently, M6G/M3G ratio was significantly higher in the two IHU groups in comparison with the non-IHU groups.

CONCLUSIONS

Chronic exposure to street heroin causes a relative increase in concentrations of the active metabolite, M6G. Since the pattern of M6G action seems closer to heroin than to morphine, the increased synthesis of M6G observed in IHU may prolong the narrow window of heroin effects.

Pharmacokinetics of morphine are not altered in subjects with Gilbert's syndrome

AIMS

To verify that Gilbert's syndrome, which is caused by decreased glucuronidation capacity of the UDP-glucuronosyl transferase (UGT)1A1, does not account for impaired morphine clearance.

METHODS

Noncompartmental pharmacokinetic parameters for morphine and its glucuronide metabolites were compared between five carriers of Gilbert's syndrome and six noncarriers after a 7.5 mg (19.8 micro mol) intravenous injection of morphine sulphate pentahydrate. To estimate the amount of morphine-6-glucuronide (M6G) formed from morphine, 1 mg of deuterized M6G was injected intravenously at the same time.

RESULTS

No differences were detected between carriers and noncarriers of Gilbert's syndrome in the clearance of morphine (80.1 +/- 12 l h(-1) vs 87.9 +/- 22 l h(-1)) and in the percentage of morphine that was metabolized to M6G (10.9 +/- 1.4 vs 13 +/- 2). The areas under the plasma concentration vs time curves of morphine, M6G and morphine-3-glucuronide also did not differ between carriers and noncarriers of Gilbert's syndrome.

CONCLUSIONS

Gilbert's syndrome is not a factor to be considered when prescribing morphine.

Encapsulation of an intrathecal catheter

A 47-year-old patient with cancer pain underwent implantation of an intrathecal drug delivery device. When the patient suffered from an infection with fever, pain on injection into the catheter and an elevated number of granulocytes in the cerebrospinal fluid 7 weeks later, radiologic examination showed an encapsulation of the catheter tip. Concentrations of morphine and morphine-6-glucuronide in the cerebrospinal fluid suggested transport of morphine into the systemic circulation via the vascularisation of the encapsulating membrane. After antibiotic therapy and removal of the catheter, morphine was administered intravenously with a one to one conversion ratio.