Comprehensive Support for Family Caregivers: Impact on Veteran Health Care Utilization and Costs.

This study aimed to examine the early impact of the Program of Comprehensive Assistance for Family Caregivers (PCAFC) on Veteran health care utilization and costs. A pre-post cohort design including a nonequivalent control group was used to understand how Veterans' use of Veteran Affairs health care and total health care costs changed in 6-month intervals up to 3 years after PCAFC enrollment. The control group was an inverse probability of treatment weighted sample of Veterans whose caregivers applied for, but were not accepted into, PCAFC. Veterans in PCAFC had similar acute care utilization postenrollment when compared with those in the control group, but significantly greater primary, specialty, and mental health outpatient care use at least 30, and up to 36, months postenrollment. Estimated total health care costs for PCAFC Veterans were $1,500 to $3,400 higher per 6-month interval than for control group Veterans. PCAFC may have increased Veterans' access to care.

Comprehensive Support for Family Caregivers of Post-9/11 Veterans Increases Veteran Utilization of Long-term Services and Supports: A Propensity Score Analysis.

Family caregivers are an important component of the long-term services and supports (LTSS) system. However, caregiving may have negative consequences for caregiver physical and emotional health. Connecting caregivers to formal short-term home- and community-based services (HCBS), through information resources and referrals, might alleviate family caregiver burden and delay nursing home entry for the patient. The aim of this study was to evaluate the early impact of the Program of Comprehensive Assistance for Family Caregivers (PCAFC) (established by P.L. 111-163 for family caregivers of seriously injured post-9/11 Veterans) on Veteran use of LTSS. A two-cohort pre-post design with a nonequivalent comparison group (treated n = 15 650; comparison n = 8339) was used to (1) examine the association between caregiver enrollment in PCAFC and any VA-purchased or VA-provided LTSS use among Veterans and (2) describe program-related trends in HCBS and institutional LTSS use. The comparison group was an inverse-propensity-score weighted sample of Veterans whose caregivers applied for, but were not accepted into, the program. From baseline through 24 months post application, use of any LTSS ranged from 13.1% to 17.8% for Veterans whose caregivers were enrolled in PCAFC versus from 3.8% to 5.3% for Veterans in the comparison group. Participation in PCAFC was associated with a statistically significant increased use of any LTSS from 1 to 24 months post application (over time odds ratios ranged from 2.71 [95% confidence interval: 2.31-3.17] to 4.86 [3.93-6.02]). Support for family caregivers may enhance utilization of LTSS for Veterans with physical, emotional, and/or cognitive conditions.

Effects of avasimibe on cytochrome P450 2C9 expression in vitro and in vivo.

Avasimibe, an acyl-CoA:cholesterol acyltransferase inhibitor, has been previously shown to be a potent inducer of CYP3A4 and multiple drug resistance protein 1. We have further characterized the drug interaction potential of avasimibe by studying the inductive and inhibitory effect of this compound on major drug-metabolizing enzymes. Enzymes known to be involved in the metabolism of drugs likely to be coadministered with avasimibe, such as CYP1A1/2, CYP2C, and CYP2B6, were evaluated further by microarray analysis, Western immunoblotting, and activity assays, using rifampicin and beta-naphthoflavone as positive controls. No change was observed in CYP1A1/2 mRNA or activity levels after avasimibe treatment. Differential induction of CYP2C9- and CYP2B6-immunoreactive protein and activity was observed depending on drug concentration and donor. Microarray analysis showed a similar increase in CYP2C and CYP2B6 mRNA levels. The inhibition potential of avasimibe on the major drug-metabolizing enzymes was assessed using pooled human liver microsomes. Avasimibe inhibited CYP2C9 (IC50 2.9 microM), CYP1A2 (IC50 13.9 microM), and CYP2C19 (IC50 26.5 microM). A clinical drug interaction study was conducted to determine whether avasimibe might interact with the CYP2C9 substrate warfarin. Volunteers received 750 mg of avasimibe and showed a 54.2% reduction in trough concentrations of S-warfarin and decreased prothrombin times by 12, 15, 19, and 21% on days 6 through 9, respectively. These results demonstrate that avasimibe's inductive spectrum resembles that of rifampin.

Regulation of CYP2B6 in primary human hepatocytes by prototypical inducers.

The objectives of this study were to evaluate the ability of 14 compounds, which differentially activate human pregnane X receptor (hPXR), to induce CYP2B6 expression and to compare CYP2B6 and CYP3A4 concentration- and time-dependent induction by select inducers. Three primary human hepatocyte preparations were treated daily for 3 days with three concentrations of all compounds. Additional concentration- and/or time-response studies were conducted with clotrimazole, phenytoin, phenobarbital, and rifampin in six preparations. CYP2B6 and CYP3A4 protein and activities were assessed by Western blotting, bupropion hydroxylation, and testosterone 6beta-hydroxylation, respectively. To evaluate hPXR activation by the 14 compounds, reporter gene assays were conducted using Huh7 cells cotransfected with hPXR and a CYP2B6 (NR1)5-LUC reporter plasmid. Clotrimazole, phenobarbital, rifampin, and ritonavir strongly induced CYP2B6 and activated hPXR; dexamethasone t-butylacetate and sulfinpyrazone induced CYP2B6 weakly and activated hPXR moderately; paclitaxel strongly activated hPXR but did not increase CYP2B6 expression; carbamazepine and phenytoin moderately or strongly increased CYP2B6 expression but weakly activated hPXR; and dexamethasone, methotrexate, probenecid, sulfadimidine, and troleandomycin demonstrated weak or negligible effects on CYP2B6 and hPXR. EC50 values for CYP2B6 and CYP3A4 induction by clotrimazole, phenobarbital, phenytoin, and rifampin were strongly correlated (r2 = 0.99) and were statistically indistinguishable for clotrimazole, phenytoin, and rifampin. Kinetic constants governing time-dependent induction by phenobarbital and rifampin were also similar between CYP2B6 and CYP3A4. These results indicate that CYP2B6 is highly inducible by known CYP3A4 inducers and suggest that hPXR is a major determinant of CYP2B6-inducible expression for many, but not all, compounds evaluated in this study.

Concurrent induction and mechanism-based inactivation of CYP3A4 by an L-valinamide derivative.

DPC 681 (N-[(3-fluorophenyl)methyl]glycyl-N-[3-[((3-aminophenyl) sulfonyl)-2-(aminophenyl)amino]-(1S,2S)-2-hydroxy-1-(phenyl-methyl)propyl]-3-methyl-l-valinamide) is a potent peptide-like human immunodeficiency virus protease inhibitor that was evaluated in phase I clinical trials. In primary cultures of hepatocytes, DPC 681 significantly induced the testosterone 6beta-hydroxylase activity of rat CYP3A, but not human CYP3A4. Western blot analysis, however, demonstrated a 3-fold increase in expression of CYP3A4 protein by 20 microM DPC 681 in primary cultures of human hepatocytes. Subsequent studies showed that DPC 681 was a potent inhibitor of human CYP3A4 (IC50 = 0.039 microM) and rat CYP3A (IC50 = 1.62 microM). Moreover, DPC 681 was a mechanism-based inactivator of CYP3A4 with KI and kinact of 0.24 microM and 0.22 min-1, respectively. Thus, DPC 681 is both a potent inhibitor and a strong inducer of CYP3A4. Induction of CYP3A4 by DPC 681 was masked in vitro by autoinactivation, similar to the protease inhibitor ritonavir. In pharmacokinetic studies in healthy human volunteers and rats, DPC 681 was found to highly autoinduce its metabolism. Human volunteers dosed with DPC 681 at 600 mg twice daily for 14 days had a 75% decrease in the mean area under the concentration-time curve and a more than 3-fold increase in apparent clearance as compared with that on day 1. Because the primary route of DPC 681 clearance is via CYP3A metabolism, the increased clearance observed in clinical studies is due to induction of human CYP3A4 expression.

Avasimibe induces CYP3A4 and multiple drug resistance protein 1 gene expression through activation of the pregnane X receptor.

In vitro and clinical studies were conducted to characterize the potential of avasimibe, an acyl-CoA/cholesterol acyltransferase inhibitor to cause drug-drug interactions. Clinically, 3- and 6-fold increases in midazolam (CYP3A4 substrate) oral clearance were observed after 50 and 750 mg of avasimibe daily for 7 days, respectively. A 40% decrease in digoxin (P-glycoprotein substrate) area under the curve was observed with 750 mg of avasimibe daily for 10 days. In vitro studies were conducted to define the mechanisms of these interactions. Induction was observed in CYP3A4 activity and immunoreactive protein (EC50 of 200-400 nM) in primary human hepatocytes treated with avasimibe. Rifampin treatment yielded similar results. Microarray analysis revealed avasimibe (1 microM) increased CYP3A4 mRNA 20-fold, compared with a 23-fold increase with 50 microM rifampin. Avasimibe induced P-glycoprotein mRNA by about 2-fold and immunoreactive protein in a dose-dependent manner. Transient transfection assays showed that avasimibe is a potent activator of the human pregnane X receptor (hPXR) and more active than rifampin on an equimolar basis. Drug-drug interaction studies for CYP3A4 using pooled human hepatic microsomes and avasimibe at various concentrations, revealed IC50 values of 20.7, 1.6, and 3.1 microM using testosterone, midazolam, and felodipine as probe substrates, respectively. Our results indicate that avasimibe causes clinically significant drug-drug interactions through direct activation of hPXR and the subsequent induction of its target genes CYP3A4 and multiple drug resistance protein 1.

Glucocorticoid receptor enhancement of pregnane X receptor-mediated CYP2B6 regulation in primary human hepatocytes.

Although the glucocorticoid receptor (GR) facilitates the xenobiotic-induced expression of CYP2B in rodents, its role in the regulation of human CYP2B6 is unclear. In this report, the role of human GR in the regulation of CYP2B6 was evaluated using primary human hepatocytes and transfection assays with Huh7 cells. CYP2B6 expression was not induced in primary hepatocytes treated with dexamethasone (DEX) concentrations (0.01-1 microM) known to activate GR. In contrast, treatment with 0.1 microM DEX enhanced CYP2B6 induction by different pregnane X receptor (PXR) activators, including rifampin, phenytoin, clotrimazole, and phenobarbital. In Huh7 cells, cotransfection of human (h)GR and hPXR with CYP2B6-phenobarbital-responsive enhancer module (PBREM) reporter constructs revealed that all hPXR ligands induce CYP2B6 reporter gene activity, and this ligand-dependent activation is greatly enhanced by activated hGR. CYP2B6 reporter gene expression was not induced in the presence of hPXR ligands when hGR alone was cotransfected with CYP2B6 reporter construct. In hGR and human constitutive androstane receptor (hCAR) cotransfection assays, activated hGR increased the constitutive activation of PBREM reporter constructs by hCAR in the absence of inducers. In the presence of activated hGR and known inducers of CYP2B6, only PB treatment caused a further 2-fold activation of hCAR compared with control. These studies show that hGR is involved synergistically in the xenobiotic-responsive regulation of human CYP2B6 by hPXR and hCAR. Moreover, the results suggest that the GR-enhanced expression of CYP2B6 is mediated through an indirect mechanism that does not require increased expression of nuclear receptor.

Comparative effects of thiazolidinediones on in vitro P450 enzyme induction and inhibition.

Rosiglitazone and pioglitazone are thiazolidinediones used for treatment of noninsulin-dependent diabetes mellitus. These compounds, along with troglitazone, were evaluated for the ability to induce cytochrome P450 enzymes (P450) in primary human hepatocyte cultures and to inhibit P450 in human microsomes. In induction studies, all three thiazolidinediones caused a dose-dependent increase in CYP3A4 activity and immunoreactive protein. While troglitazone was the most potent, rosiglitazone and pioglitazone generally exceeded troglitazone in absolute CYP3A4 activity achieved at concentrations > or =10 microM. A comparable concentration-dependent increase in CYP2B6 immunoreactive protein was observed with all three thiazolidinediones. Microarray analysis revealed rifampin > troglitazone > pioglitazone > rosiglitazone in terms of CYP3A4 mRNA induction potential with 10 microM compound. Inhibition studies conducted for CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP2A6, and CYP2E1 showed troglitazone to be the most nonselective and potent inhibitor followed by rosiglitazone and pioglitazone. In vitro, the thiazolidinediones were strong inhibitors of CYP2C8, with K(i) values between 1.7 and 5.6 microM, and of CYP3A4, with K(i) values between 1.6 and 11.8 microM. Troglitazone, in addition, inhibited CYP2C9 (K(i) 0.6 microM). Although the inhibitory effects of the thiazolidinediones have not been demonstrated clinically, our results suggest there is potential for interactions with CYP2C8 substrates. This is the first report of in vitro induction of P450 enzymes by rosiglitazone and pioglitazone. While only the induction of CYP3A4 by troglitazone has been demonstrated in vivo, these results suggest that other thiazolidinediones may have the potential to cause clinically significant drug interactions at sufficiently high doses.

CYP3A4 induction by drugs: correlation between a pregnane X receptor reporter gene assay and CYP3A4 expression in human hepatocytes.

Induction of cytochrome P450 3A4 (CYP3A4) is determined typically by employing primary culture of human hepatocytes and measuring CYP3A4 mRNA, protein and microsomal activity. Recently a pregnane X receptor (PXR) reporter gene assay was established to screen CYP3A4 inducers. To evaluate results from the PXR reporter gene assay with those from the aforementioned conventional assays, 14 drugs were evaluated for their ability to induce CYP3A4 and activate PXR. Sandwiched primary cultures of human hepatocytes from six donors were used and CYP3A4 activity was assessed by measuring microsomal testosterone 6beta-hydroxylase activity. Hepatic CYP3A4 mRNA and protein levels were also analyzed using branched DNA technology/Northern blotting and Western blotting, respectively. In general, PXR activation correlated with the induction potential observed in human hepatocyte cultures. Clotrimazole, phenobarbital, rifampin, and sulfinpyrazone highly activated PXR and increased CYP3A4 activity; carbamazepine, dexamethasone, dexamethasone-t-butylacetate, phenytoin, sulfadimidine, and taxol weakly activated PXR and induced CYP3A4 activity, and methotrexate and probenecid showed no marked activation in either system. Ritonavir and troleandomycin showed marked PXR activation but no increase (in the case of troleandomycin) or a significant decrease (in the case of ritonavir) in microsomal CYP3A4 activity. It is concluded that the PXR reporter gene assay is a reliable and complementary method to assess the CYP3A4 induction potential of drugs and other xenobiotics.

The effect of cyclophosphamide with and without dexamethasone on cytochrome P450 3A4 and 2B6 in human hepatocytes.

The purpose of this study was to characterize the concentration-response effects of cyclophosphamide (CPA) with and without dexamethasone (DEX; 10 microM) on the expression of CYP3A4 and CYP2B6 in cultured human hepatocytes at concentrations representative of standard- and high-dose CPA therapy (25 to 750 microM). CPA produced concentration-dependent increases in CYP3A4 and CYP2B6 activity and immunoreactive protein that peaked at 250 and 125 microM, respectively, and declined thereafter. The inductive effect of CPA alone and in combination with DEX was greater in magnitude for CYP2B6 compared with CYP3A4. To further examine the inductive effect of CPA on CYP3A4, CPA (250 microM) and DEX (10 microM) alone and in combination were examined in 10 hepatocyte preparations. The combination of CPA and DEX yielded higher rates of 6beta-hydroxytestosterone formation than either agent alone. However, the effect was less than additive in human hepatocyte cultures with relatively high baseline CYP3A4 activity and additive or synergistic in human hepatocyte cultures with relatively low baseline CYP3A4 activity. Induction index was highly correlated with CYP3A4 baseline activity for both CPA (r(2) = 0.75) and CPA plus DEX (r(2) = 0.85). To investigate the potential mechanism for CPA-induced increases in CYP3A4 activity, the ability of CPA alone and in combination with DEX to activate pregnane X receptor (PXR) was explored using transient transfection assays. CPA produced a dose-dependent increase in PXR activation that was maximal at the highest CPA concentration studied (500 microM). The addition of DEX to CPA resulted in a minor increase in PXR activation compared with CPA alone. These results indicate that CPA alone and in combination with DEX differentially induces the expression of CYP3A4 and 2B in a concentration-dependent manner, which may be mediated partially through activation of PXR. The impact of these effects on the efficacy and toxicity of CPA therapy warrants further investigation.