Effects of JNJ-38431055, a novel GPR119 receptor agonist, in randomized, double-blind, placebo-controlled studies in subjects with type 2 diabetes

AIM

G-protein coupled receptor agonists are currently under investigation for their potential utility in patients with type 2 diabetes mellitus (T2DM). The objective was to determine the pharmacokinetics, pharmacodynamics, safety and tolerability of GPR119 agonist, JNJ-38431055 in T2DM subjects.

METHODS

This was a randomized, double-blind, placebo- and positive-controled, single-dose cross-over study and a randomized, double-blind, placebo-controled multiple-dose parallel design study. The study was conducted at 4 US research centres. Two different experiments involving 25 and 32 different subjects were performed in male and female subjects, aged 25-60 years, mean body mass index between 22 and 39.9 kg/m2 who had T2DM diagnosed 6 months to 10 years before screening. JNJ-38431055 (100 and 500 mg) or sitagliptin (100 mg) as a single-dose or JNJ-38431055 (500 mg) once daily for 14 consecutive days were tested. Effects on stimulated plasma glucose, insulin, C-peptide and incretin concentrations were pre-specified outcomes.

RESULTS

JNJ-38431055 was well tolerated and not associated with hypoglycaemia. Plasma systemic exposure of JNJ-38431055 increased as the dose increased, was approximately two-fold greater after multiple-dose administration, and attained steady-state after approximately 8 days. Compared with placebo, single-dose administration of oral JNJ-38431055 decreased glucose excursion during an oral glucose tolerance test, but multiple-dose administration did not alter 24-h weighted mean glucose. Multiple dosing of JNJ-38431055 increased post-meal total glucagon-like peptide 1 and gastric insulinotropic peptide concentrations compared to baseline.

CONCLUSIONS

These studies provide evidence of limited glucose lowering and incretin activity for JNJ-38431055 in subjects with T2DM.

Acute antithrombotic effects of ximelagatran, an oral direct thrombin inhibitor, and r-hirudin in a human ex vivo model of arterial thrombosis

BACKGROUND

Thrombin plays a major role in thrombus formation through activation of platelets and conversion of fibrinogen to fibrin.

OBJECTIVES

To investigate the antithrombotic effects of the oral direct thrombin inhibitor (DTI) ximelagatran and the parenteral DTI r-hirudin in humans.

SUBJECTS AND METHODS

Healthy male volunteers randomized into four parallel groups each with 15 subjects received either ximelagatran (20, 40 or 80 mg orally) or r-hirudin (0.4 mg kg-1 intravenous bolus + infusion of 0.15 mg kg-1 h-1 for 2 h and 0.075 mg kg-1 h-1 for 3 h). Antithrombotic effects were assessed as changes in total thrombus area (TTA) and total fibrin area (TFA) from baseline, using the Badimon perfusion chamber model at baseline and 2 h and 5 h after drug administration.

RESULTS

Two hours postdosing, ximelagatran showed antithrombotic effects at both high and low shear rates (TTA% of mean baseline value +/- SEM was 76 +/- 13% and 71 +/- 17% [both P < 0.05] for the 20-mg dose, 85 +/- 11% [P > 0.05] and 62 +/- 15% [P < 0.05] for the 40-mg dose and 60 +/- 11% and 26 +/- 7% [both P < 0.05] for the 80-mg dose, respectively). r-Hirudin also showed a significant antithrombotic effect at high and low shear rates (76 +/- 11% [P = 0.05] and 57 +/- 17% [P < 0.05] of baseline values, 2 h postdosing, respectively). The inhibitory effects on TFA were similar to those on TTA.

CONCLUSIONS

The oral DTI ximelagatran shows antithrombotic effects under both high and low shear conditions. The antithrombotic effect of 40-80 mg ximelagatran appeared comparable to that of parenterally administered r-hirudin, which has been previously demonstrated to be clinically effective in acute coronary syndromes.

Inhibition of isoniazid-induced hepatotoxicity in rabbits by pretreatment with an amidase inhibitor

Isoniazid (INH), a widely used drug in the prophylaxis and treatment of tuberculosis, is associated with a 1 to 2% risk of severe and potentially fatal hepatotoxicity. There is evidence that the INH metabolite hydrazine plays an important role in the mechanism of this toxicity. Metabolism of INH leads to the production of hydrazine via both direct and indirect pathways. In both cases, the activity of an INH amidase is required to hydrolyze an amide bond. In the present study, using a model of INH-induced hepatotoxicity in rabbits, pretreatment of rabbits with the amidase inhibitor bis-p-nitrophenyl phosphate 30 min before injection of INH inhibited the formation of INH-derived hydrazine and decreased measures of hepatocellular damage, hepatic triglyceride accumulation, and hypertriglyceridemia. Bis-p-nitrophenyl phosphate also potently inhibited the production of hydrazine from INH in in vitro microsomal incubations (IC50 2 microM). Although hepatic glutathione stores are decreased, they are not depleted in animals with INH-induced hepatotoxicity. Significant effects on hepatic microsomal cytochrome P-450 1A1/2 and cytochrome P-450 2E1 activities suggest that these isozymes may be involved in the mechanism of the toxicity. In conclusion, this study demonstrates the importance of amidase activity in this rabbit model of hepatotoxicity and provides additional evidence in support of the role of hydrazine in the mechanism of INH-induced hepatotoxicity.

The role of l-thyroxine and hepatic reductase activity in isoniazid-induced hepatotoxicity in rabbits

There is evidence that hydrazine, a metabolite of isoniazid, plays an important role in the mechanism of isoniazid-induced hepatotoxicity. Hydrazine has been reported to be metabolised by NADPH cytochrome P-450 reductase (reductase) to reactive and potentially toxic intermediates. The present study was designed, using a model of isoniazid-induced hepatotoxicity in rabbits, to determine whether or not reductase plays a role in this toxicity. Although pretreating rabbits with l-thyroxine increased hepatic reductase activity (54% greater than controls), the severity of isoniazid-induced hepatic cell damage (plasma argininosuccinic acid lyase activity) was lower in thyroxine pre-treated animals than in animals treated with isoniazid alone (31.3+/-20 vs 56.0+/-20 Takahara Units, respectively). In addition, pre-treatment with l-thyroxine completely prevented isoniazid-induced hepatic steatosis. In conclusion, contrary to our hypothesis, an increase in reductase activity achieved by pre-treatment with l-thyroxine was associated with a decrease in the severity of isoniazid-induced hepatic cell damage and steatosis in rabbits.

A new genetic defect in human CYP2C19: mutation of the initiation codon is responsible for poor metabolism of S-mephenytoin

The 4'-hydroxylation of the S-enantiomer of the anticonvulsant drug mephenytoin exhibits a genetic polymorphism in humans. This polymorphism shows marked interracial heterogeneity, with the poor metabolizer (PM) phenotype representing 2 to 5% of Caucasian and 13 to 23% of Asian populations. Two defective CYP2C19 alleles, CYP2C19*2 and CYP2C19*3, have been described which account for approximately 87% of Caucasian and > 99% of Oriental PM alleles. The present study identifies a new allele (CYP2C19*4) in Caucasian PMs which contains an A-->G mutation in the initiation codon. A new polymerase chain reaction-restriction fragment length polymorphism genotyping test was developed, and the incidence of this allele was examined in a European Caucasian population which had been phenotyped for mephenytoin metabolism. One of nine putative PMs was heterozygous for CYP2C19*2/CYP2C19*4, which suggests that CYP2C19*4 represents a defective allele. Six of the seven remaining putative PMs available for genotyping were explained by CYP2C19*2. The frequency of the CYP2C19*4 allele in Caucasians was 0.6%. An additional Caucasian PM from a separate study was also heterozygous for CYP2C19*2 and CYP2C19*4. To verify that CYP2C19*4 represented a defective CYP2C19 allele, the initiation codon of the normal CYP2C19*1 cDNA was mutated to a GTG, and both cDNAs were expressed in yeast. Recombinant CYP2C19 protein was detected by Western blot analysis of colonies transformed with CYP2C19*1 cDNA, but not in those transformed with CYP2C19*4 cDNA. The two cDNAs were also used in an in vitro coupled transcription/translation assay. CYP2C19 protein was translated only from the CYP2C19*1 allele. These data indicate that CYP2C19*4 represents a new PM allele.

Isoniazid-induced hepatic necrosis and steatosis in rabbits: absence of effect of gender

Isoniazid, a highly effective drug for the chemoprophylaxis and treatment of tuberculosis, is associated with severe hepatotoxicity in 1-2% of individuals. In a rabbit model of isoniazid-induced hepatotoxicity, we have measured hepatic necrosis (quantitated by elevation of plasma argininosuccinic acid lyase (ASAL) activity), hepatic steatosis (quantitated by elevation of hepatic triglyceride content), and elevation in plasma triglyceride concentration in 15 rabbits. Eight of 15 rabbits were male, and 14 of 15 were rapid acetylators of sulfamethazine. Administration of isoniazid to rabbits resulted in a 27-fold increase in plasma ASAL activities, a 7.5-fold increase in hepatic triglyceride content, and a 13-fold increase in plasma triglyceride levels. This study demonstrated no effect of gender on these three pathological changes that occur in this model of isoniazid-induced hepatotoxicity in rabbits.

Role of hydrazine in the mechanism of isoniazid hepatotoxicity in rabbits

Isoniazid (INH) continues to be a highly effective drug in the chemoprophylaxis and treatment of tuberculosis; however, its use is associated with hepatotoxicity (predominantly hepatic necrosis) in 1-2% of individuals. The INH metabolites, acetylhydrazine and hydrazine, have each been implicated as the causative hepatotoxin in INH-induced hepatotoxicity. Using a model of INH-induced hepatotoxicity in rabbits, in which INH-induced hepatotoxicity manifests as hepatic necrosis, hepatic steatosis (hepatic fat accumulation) and hypertriglyceridaemia (elevated plasma triglycerides), we compared the severity of these measures of toxicity with plasma levels of INH, acetylhydrazine and hydrazine. Plasma INH and acetylhydrazine were not correlated with markers of INH-induced hepatic necrosis or fatty changes. Plasma hydrazine at 32 h was correlated significantly with plasma argininosuccinic acid lyase (ASAL, a sensitive marker of hepatic necrosis) activity as area under the curve (r2 = 0.54, P < 0.002) and log plasma ASAL activity at 48 h after the first dose of INH (r2 = 0.53, p < 0.005), but not with fatty changes. These results show in this model of INH-induced hepatotoxicity in rabbits that hydrazine, and not INH or acetylhydrazine, is most likely involved in the pathogenic mechanism of hepatic necrosis.

Hypothyroxinemia and phenytoin toxicity: a vicious circle

Phenytoin is a widely used anticonvulsant which has a relatively narrow therapeutic range of serum concentrations, 40-80 mmol/l (10-20 mg/l). Phenytoin is known to show concentration-dependent kinetics within this therapeutic range. Because of this, small changes in dose and minor alterations in hepatic metabolism of phenytoin may cause a disproportionately large affect on serum concentrations. Hypothyroidism is associated with inhibition of hepatic oxidative metabolism of many drugs. However, there is a general consensus in the literature that serum phenytoin clearance is not influenced by thyroid functional status. This report describes a 63 year-old female who developed decreased serum free T4 (8 pmol/l) and phenytoin toxicity. We identified three other similar case reports. We propose that the following vicious circle may be involved in this interaction: induction by phenytoin of hepatic enzymes involved in the metabolism of T4 and T3, decreased serum free T4 levels causing decreased activity of hepatic NADPH cytochrome P-450 reductase, a resultant decrease in hepatic P-450 IIC9 catalyzed hydroxylation of phenytoin, increased serum phenytoin concentrations and further induction of T4 and T3 hepatic metabolism.

A model of isoniazid-induced hepatotoxicity in rabbits

Isoniazid (INH) continues to be an effective drug used for chemoprophylaxis and treatment of tuberculosis. Unfortunately, INH is associated with significant hepatotoxicity in up to 2% of individuals exposed, and if this adverse event is not recognized early it can be fatal. Research on INH-induced hepatotoxicity has been hampered by the lack of a suitable animal model that closely resembles the toxicity in humans. The mechanism of INH-induced hepatotoxicity is still unknown. The present study describes the development of a reliable model of INH-induced hepatotoxicity in rabbits. The protocol involves repeated injections of INH over a 2-day period, resulting in significant hepatic necrosis as indicated by elevations of plasma argininosuccinic acid lyase activity. Pretreatment with phenobarbital increased the occurrence of INH-induced hepatic necrosis from approximately 60% (9 out of 15 rabbits) with INH alone to more than 90% (13 out of 14 rabbits). Morphological indices were used to demonstrate the presence of INH-induced hepatotoxicity, and biochemical indices were used to demonstrate both the presence and severity of INH-induced hepatotoxicity in this model. This model may prove useful for further investigations into the mechanism of INH-induced hepatotoxicity.