A selective inhibitor of cyclooxygenase-2 reverses endotoxin-induced pyretic responses in non-human primates

Central mediators involved in the febrile response: effects of antipyretic drugs

Fever is a complex signal of inflammatory and infectious diseases. It is generally initiated when peripherally produced endogenous pyrogens reach areas that surround the hypothalamus. These peripheral endogenous pyrogens are cytokines that are produced by leukocytes and other cells, the most known of which are interleukin-1β, tumor necrosis factor-α, and interleukin-6. Because of the capacity of these molecules to induce their own synthesis and the synthesis of other cytokines, they can also be synthesized in the central nervous system. However, these pyrogens are not the final mediators of the febrile response. These cytokines can induce the synthesis of cyclooxygenase-2, which produces prostaglandins. These prostanoids alter hypothalamic temperature control, leading to an increase in heat production, the conservation of heat, and ultimately fever. The effect of antipyretics is based on blocking prostaglandin synthesis. In this review, we discuss recent data on the importance of prostaglandins in the febrile response, and we show that some endogenous mediators can still induce the febrile response even when known antipyretics reduce the levels of prostaglandins in the central nervous system. These studies suggest that centrally produced mediators other than prostaglandins participate in the genesis of fever. Among the most studied central mediators of fever are corticotropin-releasing factor, endothelins, chemokines, endogenous opioids, and substance P, which are discussed herein. Additionally, recent evidence suggests that these different pathways of fever induction may be activated during different pathological conditions.

Central mediators involved in the febrile response: effects of antipyretic drugs

Fever is a complex signal of inflammatory and infectious diseases. It is generally initiated when peripherally produced endogenous pyrogens reach areas that surround the hypothalamus. These peripheral endogenous pyrogens are cytokines that are produced by leukocytes and other cells, the most known of which are interleukin-1β, tumor necrosis factor-α, and interleukin-6. Because of the capacity of these molecules to induce their own synthesis and the synthesis of other cytokines, they can also be synthesized in the central nervous system. However, these pyrogens are not the final mediators of the febrile response. These cytokines can induce the synthesis of cyclooxygenase-2, which produces prostaglandins. These prostanoids alter hypothalamic temperature control, leading to an increase in heat production, the conservation of heat, and ultimately fever. The effect of antipyretics is based on blocking prostaglandin synthesis. In this review, we discuss recent data on the importance of prostaglandins in the febrile response, and we show that some endogenous mediators can still induce the febrile response even when known antipyretics reduce the levels of prostaglandins in the central nervous system. These studies suggest that centrally produced mediators other than prostaglandins participate in the genesis of fever. Among the most studied central mediators of fever are corticotropin-releasing factor, endothelins, chemokines, endogenous opioids, and substance P, which are discussed herein. Additionally, recent evidence suggests that these different pathways of fever induction may be activated during different pathological conditions.

In vitro effects and in vivo efficacy of a novel cyclooxygenase-2 inhibitor in cats with lipopolysaccharide-induced pyrexia

OBJECTIVE

To determine cyclooxygenase (COX)-2 selectivity, pharmacokinetic properties, and in vivo efficacy of firocoxib (ML-1,785,713) in cats.

ANIMALS

5 healthy male and 14 healthy female domestic shorthair cats.

PROCEDURE

Selectivity of firocoxib for inhibiting COX-2 was determined by comparing the potency for inhibiting COX-1 with that of COX-2 in feline blood. Pharmacokinetic properties were determined after i.v. (2 mg/kg) and oral (3 mg/kg) administration in male cats. In vivo efficacy was evaluated in female cats with lipopolysaccharide (LPS)-induced pyrexia with administration of firocoxib 1 or 14 hours before LPS challenge.

RESULTS

Blood concentrations resulting in 50% inhibition of COX-1 and COX-2 activity in vitro were 75 +/- 2 microM and 0.13 +/- 0.03 microM, respectively, and selectivity for inhibiting COX-2 relative to COX-1 was 58. Firocoxib had moderate to high oral bioavailability (54% to 70%), low plasma clearance (4.7 to 5.8 mL/min/kg), and an elimination half-life of 8.7 to 12.2 hours. Firocoxib at doses from 0.75 to 3 mg/kg was efficacious in attenuating fever when administered to cats 1 or 14 hours before LPS challenge.

CONCLUSIONS AND CLINICAL RELEVANCE

Firocoxib is a potent COX-2 inhibitor and is the only selective COX-2 inhibitor described for use in cats to date. It is effective in attenuating febrile responses in cats when administered 14 hours before LPS challenge, suggesting it would be suitable for once-a-day dosing. Because selective COX-2 inhibitors have an improved therapeutic index relative to nonselective nonsteroidal anti-inflammatory drugs in humans, firocoxib has the potential to be a safe, effective anti-inflammatory agent for cats.

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.

Acetaminophen-induced hypothermia in mice is mediated by a prostaglandin endoperoxide synthase 1 gene-derived protein

Acetaminophen is a widely used antipyretic analgesic, reducing fever caused by bacterial and viral infections and by clinical trauma such as cancer or stroke. In rare cases in humans, e.g., in febrile children or HIV or stroke patients, acetaminophen causes hypothermia while therapeutic blood levels of the drug are maintained. In C57/BL6 mice, acetaminophen caused hypothermia that was dose related and maximum (>2 degrees C below normal) with a dose of 300 mg/kg. The reduction and recovery of body temperature was paralleled by a fall of >90% and a subsequent rise of prostaglandin (PG)E(2) concentrations in the brain. In cyclooxygenase (COX)-2(-/-) mice, acetaminophen (300 mg/kg) produced hypothermia accompanied by a reduction in brain PGE(2) levels, whereas in COX-1(-/-) mice, the hypothermia to this dose of acetaminophen was attenuated. The brains of COX-1(-/-) mice had approximately 70% lower levels of PGE(2) than those of WT animals, and these levels were not reduced further by acetaminophen. The putative selective COX-3 inhibitors antipyrine and aminopyrine also reduced basal body temperature and brain PGE(2) levels in normal mice. We propose that acetaminophen is a selective inhibitor of a COX-1 variant and this enzyme is involved in the continual synthesis of PGE(2) that maintains a normal body temperature. Thus, acetaminophen reduces basal body temperature below normal in mice most likely by inhibiting COX-3.

Microsomal prostaglandin E synthase-1 is a major terminal synthase that is selectively up-regulated during cyclooxygenase-2-dependent prostaglandin E2 production in the rat adjuvant-induced arthritis model

To better define the role of the various prostanoid synthases in the adjuvant-induced arthritis (AIA) model, we have determined the temporal expression of the inducible PGE synthase (mPGES-1), mPGES-2, the cytosolic PGES (cPGES/p23), and prostacyclin synthase, and compared with that of cyclooxygenase-1 (COX-1) and COX-2. The profile of induction of mPGES-1 (50- to 80-fold) in the primary paw was similar to that of COX-2 by both RNA and protein analysis. Quantitative PCR analysis indicated that induction of mPGES-1 at day 15 was within 2-fold that of COX-2. Increased PGES activity was measurable in membrane preparations of inflamed paws, and the activity was inhibitable by MK-886 to >or=90% with a potency similar to that of recombinant rat mPGES-1 (IC(50) = 2.4 microM). The RNA of the newly described mPGES-2 decreased by 2- to 3-fold in primary paws between days 1 and 15 postadjuvant. The cPGES/p23 and COX-1 were induced during AIA, but at much lower levels (2- to 6-fold) than mPGES-1, with the peak of cPGES/p23 expression occurring later than that of COX-2 and PGE(2) production. Prostacyclin (measured as 6-keto-PGF(1alpha)) was transiently elevated on day 1, and prostacyclin synthase was down-regulated at the RNA level after day 3, suggesting a diminished role of prostacyclin during the maintenance of chronic inflammation in the rat AIA. These results show that mPGES-1 is up-regulated throughout the development of AIA and suggest that it plays a major role in the elevated production of PGE(2) in this model.

Effects of selective cyclooxygenase enzyme inhibitors on lipopolysaccharide-induced dual thermoregulatory changes in rats

The effects of selective cyclooxygenase-1 and cyclooxygenase-2 inhibitors (valeryl salicylate and SC-58236, respectively) on Escherichia coli O111:B4 lipopolysaccharide (LPS)-induced dual thermoregulatory changes and serum tumor necrosis factor-alpha elevation were investigated in rats. LPS (50 microg/kg, intraperitoneal) produced an initial hypothermia that was then followed by fever. Serum tumor necrosis factor-alpha levels elevated at the initial phase of hypothermia. Valeryl salicylate injections (20, 40, and 80 mg/kg, subcutaneous [s.c.]) completely inhibited hypothermia without any effect on the elevated serum tumor necrosis factor-alpha levels and on the subsequent fever. On the other hand, SC-58236 injections (10, 20, and 40 mg/kg, s.c.) only partially abolished the hypothermia. SC-58236 had no effect on the initiation of fever, however completely inhibited the maintenance of fever. The serum tumor necrosis factor-alpha elevation was not reduced by SC-58236 treatment. The combination of valeryl salicylate and SC-58236 also failed to inhibit the initiation of fever. These findings suggest that cycloxygenase-1 may have a predominant role for the development of LPS-induced hypothermia, but cyclooxygenase-1 does not seem to be involved in the mediation of LPS-induced fever. Meanwhile, cyclooxgenase-2 may be critical for the late phase rather than the initiation of the fever response in rats.

Cyclooxygenase-two (COX-2) modulates proliferation in aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis is a locally invasive soft tissue lesion. Seventy-five per cent of cases harbor a somatic mutation in either the APC or beta-catenin genes, resulting in beta-catenin protein stabilization. Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin synthesis that modulates the formation of colonic neoplasia, especially in cases due to mutations resulting in beta-catenin stabilization. Human aggressive fibromatoses and lesions from the Apc+/Apc1638N mouse (a murine model for Apc-driven fibromatosis) demonstrated elevated COX-2 levels. COX-2 blockade either by the selective agent DFU or by non-selective COX blocking agents results in reduced proliferation in human tumor cell cultures. Breeding mice with Cox-2-/- mice resulted in no difference in number of aggressive fibromatoses formed, but in a smaller tumor size, while there was a decrease in number of GI lesions by 50%. Mice fed various COX blocking agents also showed a decline in tumor size. COX-2 expression was regulated by tcf-dependent transcription in this lesion. COX-2 partially regulates proliferation due to beta-catenin stabilization in aggressive fibromatosis. Although COX blockade alone does not cause tumor regression, this data suggests that it may have a role as an adjuvant therapy to slow tumor growth in this lesion.

Nonsteroidal anti-inflammatory drugs, acetaminophen, cyclooxygenase 2, and fever

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used antipyretic agents that most probably exert their antifever effect by inhibiting cyclooxygenase (COX)-2. Thus, COX-2-selective drugs or null mutation of the COX-2 gene reduce or prevent fever. Acetaminophen is antipyretic and analgesic, as are NSAIDs, but it lacks the anti-inflammatory and anticoagulatory properties of these drugs. This has led to the speculation that a COX variant exists that is inhibitable by acetaminophen. An acetaminophen-inhibitable enzyme is inducible in the mouse J774.2 monocyte cell line. Induction of acetaminophen-inhibitable prostaglandin E(2) synthesis parallels induction of COX-2. Thus, inhibition of pharmacologically distinct COX-2 enzyme activity by acetaminophen may be the mechanism of action of this important antipyretic drug.

COX-2 and Alzheimer's disease: potential roles in inflammation and neurodegeneration

Epidemiological and clinical data suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) are beneficial in the treatment and prevention of Alzheimer's disease (AD). NSAIDs act by inhibiting cyclooxygenase, an enzyme that occurs in constitutive and inducible isoforms, known respectively as COX-1 and COX-2. Recognition that COX-2 plays a key role in inflammation led to the hypothesis that COX-2 might represent the primary target for NSAIDs in AD, consistent with inflammatory processes occurring in AD brain. This review highlights recently gathered evidence leading to a more complex view of the role of COX-2 in AD, including evidence that COX-2 directly contributes to neuronal vulnerability. Consideration of these roles is critical for the rational implementation of NSAID therapy in AD.