Gerd Geisslinger

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti‐inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti‐inflammatory and antiproliferative effects independent of cyclooxy‐genase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF‐κB and AP‐1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKß, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF‐κB and AP‐1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARγ, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase‐independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.—Tegeder, I., Pfeilschifter, J., Geisslinger, G. Cyclooxygenase‐independent actions of cyclooxygenase inhibitors FASEB J. 15, 2057–2072 (2001)

GTP cyclohydrolase and tetrahydrobiopterin regulate pain sensitivity and persistence.

We report that GTP cyclohydrolase (GCH1), the rate-limiting enzyme for tetrahydrobiopterin (BH4) synthesis, is a key modulator of peripheral neuropathic and inflammatory pain. BH4 is an essential cofactor for catecholamine, serotonin and nitric oxide production. After axonal injury, concentrations of BH4 rose in primary sensory neurons, owing to upregulation of GCH1. After peripheral inflammation, BH4 also increased in dorsal root ganglia (DRGs), owing to enhanced GCH1 enzyme activity. Inhibiting this de novo BH4 synthesis in rats attenuated neuropathic and inflammatory pain and prevented nerve injury–evoked excess nitric oxide production in the DRG, whereas administering BH4 intrathecally exacerbated pain. In humans, a haplotype of the GCH1 gene (population frequency 15.4%) was significantly associated with less pain following diskectomy for persistent radicular low back pain. Healthy individuals homozygous for this haplotype exhibited reduced experimental pain sensitivity, and forskolin-stimulated immortalized leukocytes from haplotype carriers upregulated GCH1 less than did controls. BH4 is therefore an intrinsic regulator of pain sensitivity and chronicity, and the GTP cyclohydrolase haplotype is a marker for these traits.

COX-2 independent induction of cell cycle arrest and apoptosis in colon cancer cells by the selective COX-2 inhibitor celecoxib

The regular use of various nonsteroidal anti‐inflammatory drugs (NSAIDs) was shown to decrease the incidence of colorectal cancer. This effect is thought to be caused predominantly by inhibition of cyclooxygenase‐2 (COX‐2) and, subsequently, prostaglandin synthesis. However, recent studies have suggested that COX‐independent pathways may contribute considerably to these antiproliferative effects. To evaluate the involvement of COX‐dependent and COX‐independent mechanisms further, we assessed the effects of celecoxib (selective COX‐2 inhibitor) and SC560 (selective COX‐1 inhibitor) on cell survival, cell cycle distribution, and apoptosis in three colon cancer cell lines, which differ in their expression of COX‐2. Both drugs induced a G0/G1 phase block and reduced cell survival independent of whether or not the cells expressed COX‐2. Celecoxib was more potent than SC560. The G0/G1 block caused by celecoxib could be attributed to a decreased expression of cyclin A, cyclin B1, and cyclin‐dependent kinase‐1 and an increased expression of the cell cycle inhibitory proteins p21Waf1 and p27Kip1. In addition, celecoxib, but not SC560, induced apoptosis, which was also independent of the COX‐2 expression of the cells. In vivo, celecoxib as well as SC560 reduced the proliferation of HCT‐15 (COX‐2 deficient) colon cancer xenografts in nude mice, but both substances had no significant effect on HT‐29 tumors, which express COX‐2 constitutively. Thus, our in vitro and in vivo data indicate that the antitumor effects of celecoxib probably are mediated through COX‐2 independent mechanisms and are not restricted to COX‐2 over‐expressing tumors.

Analgesic effects of morphine and morphine-6-glucuronide in a transcutaneous electrical pain model in healthy volunteers.

Our objective was to quantify the extent and time course of the effects of morphine‐6‐glucuronide and morphine on pain threshold, pain tolerance, pupil diameter, and side effects.

Chain length-specific properties of ceramides.

Ceramides are a class of sphingolipids that are abundant in cell membranes. They are important structural components of the membrane but can also act as second messengers in various signaling pathways. Until recently, ceramides and dihydroceramides were considered as a single functional class of lipids and no distinction was made between molecules with different chain lengths. However, based on the development of high-throughput, structure-specific and quantitative analytical methods to measure ceramides, it has now become clear that in cellular systems the amounts of ceramides differ with respect to their chain length. Further studies have indicated that some functions of ceramides are chain-length dependent. In this review, we discuss the chain length-specific differences of ceramides including their pathological impact on Alzheimers disease, inflammation, autophagy, apoptosis and cancer.

Pharmacokinetics of Opioids in Liver Disease

The liver is the major site of biotransformation for most opioids. Thus, the disposition of these drugs may be affected in patients with liver insufficiency. The major metabolic pathway for most opioids is oxidation. The exceptions are morphine and buprenorphine, which primarily undergo glucuronidation, and remifentanil, which is cleared by ester hydrolysis.Oxidation of opioids is reduced in patients with hepatic cirrhosis, resulting in decreased drug clearance [for pethidine (meperidine), dextropropoxyphene, pentazocine, tramadol and alfentanil] and/or increased oral bioavailability caused by a reduced first-pass metabolism (for pethidine, dextropropoxyphene, pentazocine and dihydrocodeine). Although glucuronidation is thought to be less affected in liver cirrhosis, the clearance of morphine was found to be decreased and oral bioavailability increased.The consequence of reduced drug metabolism is the risk of accumulation in the body, especially with repeated administration. Lower doses or longer administration intervals should be used to remedy this risk. Special risks are known for pethidine, with the potential for the accumulation of norpethidine, a metabolite that can cause seizures, and for dextropropoxyphene, for which several cases of hepatotoxicity have been reported. On the other hand, the analgesic activity of codeine and tilidine depends on transformation into the active metabolites, morphine and nortilidine, respectively. If metabolism is decreased in patients with chronic liver disease, the analgesic action of these drugs may be compromised. Finally, the disposition of a few opioids, such as fentanyl, sufentanil and remifentanil, appears to be unaffected in liver disease.

The polymorphism A118G of the human mu-opioid receptor gene decreases the pupil constrictory effect of morphine-6- glucuronide but not that of morphine

Large individual differences in the clinical response to morphine therapy have been known for a long time by clinicians. The recent advances in genomic research encourage the search for pharmacogenetic causes of that variability. As a measure of central opioid effects, pupil diameters were assessed every 20 min for 18 h after administration of morphine or its active metabolite morphine-6-glucuronide (M6G) in a two-way crossover study. The opioid effects were compared between six subjects with a single-nucleotide polymorphism (SNP) A118G in the mu-opioid receptor gene (five heterozygous, one homozygous) and six control subjects. Non-parametric pharmacokinetic-pharmacodynamic modelling was employed to identify the influence of the A118G SNP on the concentration-response relationship of M6G and morphine, which was described by a sigmoid Emax model. As a measure of potency, the EC50 of the pupil constrictory effects of M6G was 714 +/- 197 nmol/l in wild-type and 1475 +/- 424 nmol/l in heterozygous carriers of the A118G SNP. In the homozygous carrier of the SNP, it had an EC50 of 3140 nmol/l. In addition, the dose-response relationship was flatter in the A118G carriers than in control subjects (shape factor of the sigmoid Emax model: gamma = 3.3 +/- 1.2, 1.7 +/- 0.5 and 1.6 for wild-type, heterozygous and the homozygous A118G carriers, respectively). In contrast, the concentration-response relationship of morphine was not affected by this specific SNP. The A118G SNP in the mu-receptor gene significantly reduces the potency of M6G in humans.

Ziconotide for treatment of severe chronic pain

Pharmacological management of severe chronic pain is difficult to achieve with currently available analgesic drugs, and remains a large unmet therapeutic need. The synthetic peptide ziconotide has been approved by the US Food and Drug Administration and the European Medicines Agency for intrathecal treatment of patients with severe chronic pain that is refractory to other treatment modalities. Ziconotide is the first member in the new drug class of selective N-type voltage-sensitive calcium-channel blockers. The ziconotide-induced blockade of N-type calcium channels in the spinal cord inhibits release of pain-relevant neurotransmitters from central terminals of primary afferent neurons. By this mechanism, ziconotide can effectively reduce pain. However, ziconotide has a narrow therapeutic window because of substantial CNS side-effects, and thus treatment with ziconotide is appropriate for only a small subset of patients with severe chronic pain. We provide an overview of the benefits and limitations of intrathecal ziconotide treatment and review potential future developments in this new drug class.

Opioids As Modulators of Cell Death and Survival—Unraveling Mechanisms and Revealing New Indications

Opioids are powerful analgesics but also drugs of abuse. Because opioid addicts are susceptible to certain infections, opioids have been suspected to suppress the immune response. This was supported by the finding that various immune-competent cells express opioid receptors and undergo apoptosis when treated with opioid alkaloids. Recent evidence suggests that opioids may also effect neuronal survival and proliferation or migrating properties of tumor cells. A multitude of signaling pathways has been suggested to be involved in these extra-analgesic effects of opioids. Growth-promoting effects were found to be mediated through Akt and Erk signaling cascades. Death-promoting effects have been ascribed to inhibition of nuclear factor-κB, increase of Fas expression, p53 stabilization, cytokine and chemokine release, and activation of nitric oxide synthase, p38, and c-Jun-N-terminal kinase. Some of the observed effects were inhibited with opioid receptor antagonists or pertussis toxin; others were unaffected. It is still unclear whether these properties are mediated through typical opioid receptor activation and inhibitory G-protein-signaling. The present review tries to unravel controversial findings and provides a hypothesis that may help to integrate diverse results.

Genetic predictors of the clinical response to opioid analgesics: Clinical utility and future perspectives

This review uses a candidate gene approach to identify possible pharmacogenetic modulators of opioid therapy, and discusses these modulators together with demonstrated genetic causes for the variability in clinical effects of opioids.Genetically caused inactivity of cytochrome P450 (CYP) 2D6 renders codeine ineffective (lack of morphine formation), slightly decreases the efficacy of tramadol (lack of formation of the active O-desmethyl-tramadol) and slightly decreases the clearance of methadone. MDR1 mutations often demonstrate pharmacogenetic consequences, and since Opioids are among the P-glycoprotein substrates, opioid pharmacology may be affected by MDR1 mutations. The single nucleotide polymorphism A118G of the μ opioid receptor gene has been associated with decreased potency of morphine and morphine-6-glucuronide, and with decreased analgesic effects and higher alfentanil dose demands in carriers of the mutated Gl 18 allele. Genetic causes may also trigger or modify drug interactions, which in turn can alter the clinical response to opioid therapy. For example, by inhibiting CYP2D6, paroxetine increases the steady-state plasma concentrations of (R)-methadone in extensive but not in poor metabolisers of debrisoquine/sparteine.So far, the clinical consequences of the pharmacogenetics of opioids are limited to codeine, which should not be administered to poor metabolisers of debrisoquine/sparteine. Genetically precipitated drug interactions might render a standard opioid dose toxic and should, therefore, be taken into consideration. Mutations affecting opioid receptors and pain perception/processing are of interest for the study of opioid actions, but with modern practice of on-demand administration of Opioids their utility may be limited to explaining why some patients need higher opioid doses; however, the adverse effects profile may be modified by these mutations. Nonetheless, at a limited level, pharmacogenetics can be expected to facilitate individualised opioid therapy.