Pharmacokinetic-pharmacodynamic modelling of the analgesic effects of lumiracoxib, a selective inhibitor of cyclooxygenase-2, in rats

The early inhibition of the COX-2 pathway in viperid phospholipase A2-induced skeletal muscle myotoxicity accelerates the tissue regeneration

The administration of non-steroidal anti-inflammatory drugs in the treatment of injury and muscle regeneration is still contradictory in effectiveness, especially regarding the timing of their administration. This can interfere with the production of prostaglandins originating from inflammatory isoform cyclooxygenase-2 (COX-2), which is essential to modulate tissue regeneration. The phospholipases A₂ (PLA₂) from viperid venoms cause myotoxicity, therefore constituting a tool for the study of supportive therapies to improve skeletal muscle regeneration. This study investigated the effect of early administration of lumiracoxib (selective inhibitor of COX-2) on the degeneration and regeneration stages of skeletal muscle after injury induced by a myotoxic PLA₂. After 30 min and 48 h of intramuscular injection of PLA₂, mice received lumiracoxib orally and histological, functional, and transcriptional parameters of muscle were evaluated from 6 h to 21 days. Inhibition of COX-2 in the early periods of PLA₂-induced muscle degeneration reduced leukocyte influx, edema, and tissue damage. After the second administration of lumiracoxib, in regenerative stage, muscle showed increase in number of basophilic fibers, reduction in fibrosis content and advanced recovery of functionality characterized by the presence of fast type II fibers. The expression of Pax7 and myogenin were increased, indicating a great capacity for storing satellite cells and advanced mature state of tissue. Our data reveals a distinct role of COX-2-derived products during muscle degeneration and regeneration, in which early administration of lumiracoxib was a therapeutic strategy to modulate the effects of prostaglandins, providing a breakthrough in muscle tissue regeneration induced by a myotoxic PLA_2.

Semi-mechanistic modelling of the analgesic effect of gabapentin in the formalin-induced rat model of experimental pain

PURPOSE

The formalin-induced rat model of nociception involves moderate continuous pain. Formalin-induced pain results in a typical repetitive flinching behaviour, which displays a biphasic pattern characterised by peaks of pain. Here we described the time course of pain response and the analgesic effect of gabapentin using a semi-mechanistic modelling approach.

METHODS

Male Sprague-Dawley rats received gabapentin (10-100 mg/kg) or placebo 1 h prior to the formalin injection, as per standard protocol. A reduction in the frequency of the second peak of flinching was used as a behavioural measure of gabapentin-mediated anti-nociception. The flinching response was modelled using a mono-exponential function to characterise the first peak and an indirect response model with a time variant synthesis rate for the second. PKPD modelling was performed using a population approach in NONMEM v.7.1.2.

RESULTS

The time course of the biphasic response was adequately described by the proposed model, which included separate expressions for each phase. Gabapentin was found to reversibly decrease, but not suppress the flinching frequency of the second response peak only. The mean IC50 estimate was 7,510 ng/ml, with relative standard error (RSE%) of 40%.

CONCLUSIONS

A compartmental, semi-mechanistic model provides the basis for further understanding of the formalin-induced flinching response and consequently to better characterisation of the properties of gabapentin, such as the potency in individual animals. Moreover, despite high exposure levels, model predictions show that gabapentin does not completely suppress behavioural response in the formalin-induced pain model.

Semi-mechanistic modeling of the interaction between the central and peripheral effects in the antinociceptive response to lumiracoxib in rats

The model-based approach was undertaken to characterize the interaction between the peripheral and central antinociceptive effects exerted by lumiracoxib. The effects of intraplantar and intrathecal administrations and of fixed ratio combinations of lumiracoxib simultaneously administered by these two routes were evaluated using the formalin test in rats. Pain-related behavior data, quantified as the number of flinches of the injected paw, were analyzed using a population approach with NONMEM 7. The pain response during the first phase of the formalin test, which was insensitive to lumiracoxib, was modeled using a monoexponential decay. The second phase, which was sensitive to lumiracoxib, was described incorporating synthesis and degradation processes of pain mediators that were recruited locally after tissue injury. Upregulation at the local level and in the central nervous system (CNS) was set to be proportional to the predicted levels of pain mediators in the local (injured) compartment. Results suggest a greater role of upregulated COX-2(Local) in generating the pain response compared to COX-2(CNS). Drug effects were described as inhibition of upregulated COX-2. The model adequately described the time course of nociception after formalin injection in the absence or presence of lumiracoxib administered locally and/or spinally. Data suggest that the overall response is the additive outcome of drug effects at the peripheral and central compartments, with predominance of peripheral mechanisms. Application of modeling opens new perspectives for understanding the overall mechanism of action of analgesic drugs.

Pharmacokinetic-pharmacodynamic modeling of diclofenac in normal and Freund's complete adjuvant-induced arthritic rats

AIM

To characterize pharmacokinetic-pharmacodynamic modeling of diclofenac in Freund's complete adjuvant (FCA)-induced arthritic rats using prostaglandin E(2) (PGE(2)) as a biomarker.

METHODS

The pharmacokinetics of diclofenac was investigated using 20-day-old arthritic rats. PGE(2) level in the rats was measured using an enzyme immunoassay. A pharmacokinetic-pharmacodynamic (PK-PD) model was developed to illustrate the relationship between the plasma concentration of diclofenac and the inhibition of PGE(2) production. The inhibition of diclofenac on lipopolysaccharide (LPS)-induced PGE(2) production in blood cells was investigated in vitro.

RESULTS

Similar pharmacokinetic behavior of diclofenac was found both in normal and FCA-induced arthritic rats. Diclofenac significantly decreased the plasma levels of PGE(2) in both normal and arthritic rats. The inhibitory effect on PGE(2) levels in the plasma was in proportion to the plasma concentration of diclofenac. No delay in the onset of inhibition was observed, suggesting that the effect compartment was located in the central compartment. An inhibitory effect sigmoid I(max) model was selected to characterize the relationship between the plasma concentration of diclofenac and the inhibition of PGE(2) production in vivo. The I(max) model was also used to illustrate the inhibition of diclofenac on LPS-induced PGE(2) production in blood cells in vitro.

CONCLUSION

Arthritis induced by FCA does not alter the pharmacokinetic behaviors of diclofenac in rats, but the pharmacodynamics of diclofenac is slightly affected. A PK-PD model characterizing an inhibitory effect sigmoid I(max) can be used to fit the relationship between the plasma PGE(2) and diclofenac levels in both normal rats and FCA-induced arthritic rats.

Role of ATP-sensitive K+ channels in the antinociception induced by non-steroidal anti-inflammatory drugs in streptozotocin-diabetic and non-diabetic rats

There is evidence that systemic sulfonylureas block diclofenac-induced antinociception in normal rat, suggesting that diclofenac activates ATP-sensitive K(+) channels. However, there is no evidence for the systemic interaction between different non-steroidal anti-inflammatory drugs (NSAIDs) and sulfonylureas in streptozotocin (STZ)-diabetic rats. Therefore, this work was undertaken to determine whether two sulfonylureas, glibenclamide and glipizide, have any effect on the systemic antinociception that is induced by diclofenac (30 mg/kg), lumiracoxib (56 mg/kg), meloxicam (30 mg/kg), metamizol (56 mg/kg) and indomethacin (30 mg/kg) using the non-diabetic and STZ-diabetic rat formalin test. Systemic injections of NSAIDs produced dose-dependent antinociception during the second phase of the test in both non-diabetic and STZ-diabetic rats. Systemic pretreatment with glibenclamide (10 mg/kg) and glipizide (10 mg/kg) blocked diclofenac-induced systemic antinociception in the second phase of the test (P<0.05) in both non-diabetic and STZ-diabetic rats. In contrast, pretreatment with glibenclamide or glipizide did not block lumiracoxib-, meloxicam-, metamizol-, and indomethacin-induced systemic antinociception (P>0.05) in both groups. Results showed that systemic NSAIDs are able to produce antinociception in STZ-diabetic rats. Likewise, data suggest that diclofenac, but not other NSAIDs, activated K(+) channels to induce its systemic antinociceptive effect in the non-diabetic and STZ-diabetic rat formalin test.

Pharmacokinetic/pharmacodynamic modeling in inflammation

Inflammation is an array of immune responses to infection and injury. It results from a complex immune cascade and is the basis of many chronic diseases such as arthritis, diabetes, and cancer. Numerous mathematical models have been developed to describe the disease progression and effects of anti-inflammatory drugs. This review illustrates the state of the art in modeling the effects of diverse drugs for treating inflammation, describes relevant biomarkers amenable to modeling, and summarizes major advantages and limitations of the published pharmacokinetic/ pharmacodynamic (PK/PD) models. Simple direct inhibitory models are often used to describe in vitro effects of anti-inflammatory drugs. Indirect response models are more mechanism based and have been widely applied to the turnover of symptoms and biomarkers. These, along with target-mediated and transduction models, have been successfully applied to capture the PK/PD of many anti-inflammatory drugs and describe disease progression of inflammation. Biologics have offered opportunities to address specific mechanisms of action, and evolve small systems models to quantitatively capture the underlying physiological processes. More advanced mechanistic models should allow evaluation of the roles of some key mediators in disease progression, assess drug interactions, and better translate drug properties from in vitro and animal data to patients.