Characterizing the PK/PD relationship for inhibition of capsaicin-induced dermal vasodilatation by MK-3207, an oral calcitonin gene related peptide receptor antagonist

Aims

Calcitonin gene related peptide (CGRP) receptor antagonists are effective acute migraine treatments. A capsaicin-induced dermal vasodilatation (CIDV) model has been developed to provide target-engagement information in healthy volunteers. In the model, CGRP release is provoked after dermal capsaicin application, by activating transient receptor potential vanilloid-type-1 (TRPV1) receptors at peripheral sensory nerves. Laser Doppler imaging is used to quantify CIDV and subsequent inhibition by CGRP receptor antagonists. We sought to evaluate a CGRP receptor antagonist, MK-3207, in the biomarker model and to assess the predictability of the CIDV response to migraine clinical efficacy.

Methods

An integrated population pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the exposure−response relationship for CIDV inhibition by CGRP and TRPV1 receptor antagonists. MK-3207 dose−response predictions were made based on estimated potency from the PK/PD model and mean plasma concentrations observed at the doses investigated.

Results

The results suggested that a 20 mg dose of MK-3207 (EC₅₀ of 1.59 nm) would be required to attain the peripheral CIDV response at a target level that was shown previously to correlate with 2 h clinical efficacy based on phase 3 telcagepant clinical data, and that a plateau of the dose−response would be reached around 40–100 mg. These predictions provided a quantitative rationale for dose selection in a phase 2 clinical trial of MK-3207 and helped with interpretation of the efficacy results from the trial.

Conclusions

The integrated CIDV PK/PD model provides a useful platform for characterization of PK/PD relationships and predictions of dose−response relationships to aid in future development of CGRP and TRPV1 receptor antagonists.     

ΔFosB Induction in Prefrontal Cortex by Antipsychotic Drugs is Associated with Negative Behavioral Outcomes

ΔFosB, a FosB gene product, is induced in the prefrontal cortex (PFC) by repeated exposure to several stimuli including antipsychotic drugs such as haloperidol. However, the functional consequences of increased ΔFosB expression following antipsychotic treatment have not been explored. Here, we assessed whether ΔFosB induction by haloperidol mediates the positive or negative consequences or clinical-related actions of antipsychotic treatment. We show that individuals with schizophrenia who were medicated with antipsychotic drugs at their time of death display increased ΔFosB levels in the PFC, an effect that is replicated in rats treated chronically with haloperidol. In contrast, individuals with schizophrenia who were medication-free did not exhibit this effect. Viral-mediated overexpression of ΔFosB in the PFC of rodents induced cognitive deficits as measured by inhibitory avoidance, increased startle responses in prepulse inhibition tasks, and increased MK-801-induced anxiety-like behaviors. Together, these results suggest that ΔFosB induction in the PFC by antipsychotic treatment contributes to the deleterious effects of these drugs and not to their therapeutic actions.     

MK-801 prevents overexpression of multidrug resistance protein 2 after status epilepticus

Abstract

Objective: The aim of this study was to investigate whether NMDA receptor was involved in the upregulation of multidrug resistance protein 2 (Mrp2) expression during status epilepticus (SE).

Methods: The alterations in the expression of Mrp2 at various time points after SE, and the inhibition of glutamate N-methyl-D-aspartate (NMDA) receptor on Mrp2 expression in hippocampus were both tested by quantitative real-time polymerase chain reaction and western blot. Moreover, immunofluorescence was also used to analyze the impact of the NMDA receptor antagonist, MK-801, on the distribution of Mrp2 in different brain areas.

Results: The results showed that gene encoding Mrp2 was upregulated in hippocampus at 6 hours after the end of SE, and this initial increase was followed by gradual normalization. While between 3 and 72 hours after the end of SE, the protein level of Mrp2 was upregulated in hippocampus, with the highest level emerging at 24 hours. The increment of Mrp2 gene and protein induced by SE was prevented by MK-801 at 6 and 24 hours respectively after the end of SE in the hippocampus. Moreover, immunofluorescence showed that seizures-induced increase of Mrp2 expression was attenuated by the administration of MK-801 mainly in capillaries. Rats after SE exhibited a significant upregulation of Mrp2 in the capillary endothelial cells of the cerebral cortex, piriform cortex, and hippocampus, compared with those in control at 24 hours after the end of SE.

Conclusion: The results indicated that the NMDA receptor plays an important role in the upregulation of Mrp2 expression in the blood–brain barrier.     

Efficacy and safety of the dipeptidyl peptidase-4 inhibitor, sitagliptin, in patients with type 2 diabetes mellitus inadequately controlled on glimepiride alone or on glimepiride and metformin

AIM: To assess the efficacy and safety of a 24-week treatment with sitagliptin, a highly selective once-daily oral dipeptidyl peptidase-4 (DPP-4) inhibitor, in patients with type 2 diabetes who had inadequate glycaemic control [glycosylated haemoglobin (HbA(1c)) >or=7.5% and or=4 mg/day) monotherapy and 229 were on glimepiride (>or=4 mg/day) plus metformin (>or=1,500 mg/day) combination therapy. Patients exceeding pre-specified glycaemic thresholds during the double-blind treatment period were provided open-label rescue therapy (pioglitazone) until study end. The primary efficacy analysis evaluated the change in HbA(1c) from baseline to Week 24. Secondary efficacy endpoints included fasting plasma glucose (FPG), 2-h post-meal glucose and lipid measurements. RESULTS: Mean baseline HbA(1c) was 8.34% in the sitagliptin and placebo groups. After 24 weeks, sitagliptin reduced HbA(1c) by 0.74% (p < 0.001) relative to placebo. In the subset of patients on glimepiride plus metformin, sitagliptin reduced HbA(1c) by 0.89% relative to placebo, compared with a reduction of 0.57% in the subset of patients on glimepiride alone. The addition of sitagliptin reduced FPG by 20.1 mg/dl (p < 0.001) and increased homeostasis model assessment-beta, a marker of beta-cell function, by 12% (p < 0.05) relative to placebo. In patients who underwent a meal tolerance test (n = 134), sitagliptin decreased 2-h post-prandial glucose (PPG) by 36.1 mg/dl (p < 0.001) relative to placebo. The addition of sitagliptin was generally well tolerated, although there was a higher incidence of overall (60 vs. 47%) and drug-related adverse experiences (AEs) (15 vs. 7%) in the sitagliptin group than in the placebo group. This was largely because of a higher incidence of hypoglycaemia AEs (12 vs. 2%, respectively) in the sitagliptin group compared with the placebo group. Body weight modestly increased with sitagliptin relative to placebo (+0.8 vs. -0.4 kg; p < 0.001). CONCLUSIONS: Sitagliptin 100 mg once daily significantly improved glycaemic control and beta-cell function in patients with type 2 diabetes who had inadequate glycaemic control with glimepiride or glimepiride plus metformin therapy. The addition of sitagliptin was generally well tolerated, with a modest increase in hypoglycaemia and body weight, consistent with glimepiride therapy and the observed degree of glycaemic improvement.     

Brain Neuronal Degeneration Caused by Episodic Alcohol Intoxication in Rats: Effects of Nimodipine, 6,7-Dinitro-quinoxaline-2,3-dione, and MK-801

Rats repeatedly intoxicated with alcohol (ethanol, three times daily) over a 4-day period display neuronal degeneration in the dentate gyrus; entorhinal, piriform, insular, orbital, and perirhinal cortices; and in the olfactory nerve fibers and terminals in the olfactory bulb. Postulating a role for excitotoxicity, we have attempted to prevent the degeneration using antagonists that are neuroprotective in this type of brain damage. In an initial study, continuous subcutaneous infusion of a high dose of the glutamate/NMDA receptor antagonist MK-801 (2 mg/kg/day) by itself caused extensive neuronal degeneration in several brain regions and severe behavioral intoxication that precluded survival if combined with high blood alcohol levels (～300 mg/dl). Moreover, the lower, nonneurotoxic blood alcohol levels (～150 mg/dl) that were compatible with survival worsened the MK-801-induced brain damage. In a subsequent experiment, daily intraperitoneal injections of a lower dose of MK-801 (1 mg/kg/day) resulted in no MK-801 toxicity and, when combined with neurotoxic levels of alcohol, no reduction in alcohol-induced neurotoxicity. Nimodipine, a voltage-gated Ca²⁺ channel blocker, reduced the neuronal damage in the dentate gyrus, but greatly increased it in the piriform cortex when administered intragastrically at 600 mg/kg/day; it provided no protection from alcohol-dependent degeneration when given intragastrically at 100 mg/kg/day. Continuous intracere-broventricular delivery of 0.24 to 0.29 mg/day of 6,7-dinitro-quinoxa-line-2,3-dione, a glutamate/α-amino-3-hydroxy-5-methyl-4-isoxazole receptor antagonist, failed to diminish alcohol-dependent neuronal damage in any brain region. We conclude that brain damage from episodic “binge” alcohol intoxication is not primarily mediated by excitotoxic mechanisms, implying that other, nonexcrtotoxic pathophysiological mechanisms, are involved. Furthermore, MK-801, far from protecting from the alcohol-induced damage, at high doses causes widespread neuropathology that is significantly potentiated by alcohol.     

Effect of adding sitagliptin, a dipeptidyl peptidase-4 inhibitor, to metformin on 24-h glycaemic control and beta-cell function in patients with type 2 diabetes

AIM: The aim of this study was to assess the effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on 24-h glucose control when added to the regimen of patients with type 2 diabetes who had inadequate glycaemic control on metformin therapy. METHODS: In a double-blind, randomized, placebo-controlled, two-period crossover study, patients with type 2 diabetes with inadequate glycaemic control on metformin monotherapy (i.e. on a stable dose of > or = 1500 mg/day for > or = 6 weeks prior to the screening visit and an haemoglobin A(1c) (HbA(1c)) > or = 6.5% and <10% and fasting plasma glucose (FPG) < or = 240 mg/dl) were recruited for participation. A total of 28 patients (baseline HbA(1c) range = 6.5-9.6%) receiving metformin were randomized into one of two treatment sequences: the addition of placebo for 4 weeks followed by the addition of sitagliptin 50 mg twice daily (b.i.d.) for 4 weeks, or vice versa. At the end of each treatment period, patients were domiciled for frequent blood sampling over 24 h. The primary endpoint was 24-h weighted mean glucose (WMG) and secondary endpoints included change in FPG, mean of 7 daily self-blood glucose measurements (MDG) and fructosamine. beta-cell function was assessed from glucose and C-peptide concentrations were measured during the 5-h period after a standard breakfast meal by using the C-peptide minimal model. RESULTS: Despite a carryover effect from period 1 to period 2, the combined period 1 and period 2 results for glycaemic endpoints were statistically significant for sitagliptin relative to placebo when added to ongoing metformin therapy. To account for the carryover effect, the period 1 results were also compared between the groups. Following period 1, there were significant least-squares (LS) mean reductions in 24-h WMG of 32.8 mg/dl, significant LS mean reduction from baseline in MDG of 28 mg/dl, FPG of 20.3 mg/dl and fructosamine of 33.7 mmol/l in patients treated with sitagliptin relative to placebo (p < 0.05). When added to ongoing metformin therapy, parameters of beta-cell function were significantly improved with sitagliptin compared with placebo. No weight gain or increases in gastrointestinal adverse events or hypoglycaemia events were observed with sitagliptin relative to placebo during this study. CONCLUSIONS: In this study, the addition of sitagliptin 50 mg b.i.d. to ongoing metformin therapy improved 24-h glycaemic control and beta-cell function, and was generally well tolerated in patients with type 2 diabetes.     

MK-801对利多卡因致大鼠惊厥效应的影响

目的研究MK-801对利多卡因致大鼠中毒惊厥作用及其机制。方法 Wistar雄性大鼠22只,随机分为对照组(C组,n=6)、利多卡因组(L组,n=8)和MK-801组(M组,n=8)。C组腹腔注射生理盐水0.5 ml/kg,30 min后泵入复方乳酸钠。L组和M组腹腔分别注射生理盐水0.5ml/kg和MK-801 0.5 mg/kg,30 min后静注2%利多卡因2 mg,继以4 mg.kg-1.min-1持续泵入,惊厥波出现后停止泵入利多卡因,记录惊厥波发生及持续时间,呼吸抑制及持续时间。观察N-甲基-D-天门冬氨酸受体1(NMDAR1)免疫阳性细胞活性变化,测定泵注后20、30、40、50、60 min海马CA1区细胞外液谷氨酸(Glu)和γ-氨基丁酸(GABA)浓度。结果 C组未出现惊厥波,L组均出现惊厥波,M组2只大鼠出现惊厥波。与L组比较,M组呼吸抑制出现较晚(P<0.05),呼吸抑制持续时间较短(P<0.05)。与C组比较,L组和M组NMDAR1免疫阳性细胞数均显著增多(P<0.05),L组显著多于M组(P<0.05)。泵注后30、40、50、60 min L组Glu浓度显著高于C组和M组(P<0...