Risk Assessment for Hepatobiliary Toxicity Liabilities in Drug Development.

Risk assessment of hepatobiliary toxicities represents one of the greatest challenges and, more often than not, one of the most rewarding activities in which toxicologic pathologists can partake, and often times lead. This is in part because each liver toxicity picture is a bit different, informed by a broad range and diversity of relevant data, and also in part because the heavily relied upon animal models are imperfect regarding predictivity of hepatic effects in humans. Following identification and characterization of a hepatotoxicity hazard, typically in nonclinical toxicology studies, a holistic and integrated assessment of liver-relevant endpoints is conducted that typically incorporates ADME (absorption, distribution, metabolism, and excretion) information (ideally, including extensive transporter data, exposure margins, and possibly concentration of parent/metabolite at region of injury), target expression/function, in silico prediction data, in vitro hepatocyte data, liver/circulating biomarkers, and importantly, species specificity of any of these data. Of course, a thorough understanding, developed in close partnership with clinical colleagues, of the anticipated liver disease status of intended patient populations is paramount to hepatic risk assessment. This is particularly important since the likelihood of translatable determinant hepatic events observed in nonclinical models to occur in humans has been reasonably well established.

Hepatic Phospholipidosis Is Associated with Altered Hepatobiliary Function as Assessed by Gadoxetate Dynamic Contrast-enhanced Magnetic Resonance Imaging.

To determine if amiodarone induces hepatic phospholipidosis (PLD) sufficient to detect changes in hepatobiliary transporter function as assessed by gadoxetate dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), rats were orally dosed with vehicle (1% methyl cellulose) or amiodarone (300 mg/kg/day) for 7 consecutive days. Gadoxetate DCE-MRI occurred at baseline, day 7, and following a 2-week washout of amiodarone. At day 7, the gadoxetate washout rate was significantly decreased compared to the vehicle group. Blood chemistry analysis revealed no significant changes in liver enzymes (alanine aminotransferase [ALT]/aspartate aminotransferase [AST]/alkaline phosphatase [ALP]), bilirubin, or bile acids between vehicle or amiodarone groups. Hepatic PLD was confirmed in all rats treated with amiodarone at day 7 by transmission electron microscopy. Following the 2-week washout, there was no ultrastructural evidence of hepatic PLD in rats and the gadoxetate washout rate returned to baseline levels. This is the first study to show the application of gadoxetate DCE-MRI to detect hepatobiliary functional changes associated with PLD and offer a potential new technique with clinical utility in patients suspected of having PLD. These results also suggest PLD itself has functional consequences on hepatobiliary function in the absence of biomarkers of toxicity, given the cause/effect relationship between PLD and function has not been fully established.

Acute Alpha-Naphthylisothiocyanate-induced Liver Toxicity in Germfree and Conventional Male Rats.

Differences in the responses of conventional and germfree male Sprague-Dawley rats to acute injury induced by alpha-naphthylisothiocyanate (ANIT), a well-characterized biliary epithelial toxicant, were evaluated. Conventional and germfree rats were dosed once orally with 50 mg/kg of ANIT or corn oil alone and serially sacrificed daily for the next 3 days. Germfree rats treated with ANIT tended to have greater increases in virtually all liver and biliary-related analytes compared with conventional rats treated with ANIT; however, significant differences were found only in a few of these analytes including increased bile acids on day 3, total bilirubin on day 4, glutamate dehydrogenase (GLDH) on day 3, and reduced paraoxonase 1 (PON1) on days 2 and 3. Histologic differences between the conventional and germfree rats were modest, but most pronounced on day 2 (24-hr post dosing). Based on subjective scoring, biliary necrosis, neutrophilic cholangitis, and portal tract edema were more severe in germfree rats at 24 hr post dosing compared with conventional rats. Biliary epithelial replication did not differ between treated groups, however. Overall, germfree rats had a modestly greater level of biliary tract injury based on subjective histologic scoring and clinical chemistry measurements following an acute exposure to the well-characterized biliary toxin, ANIT; however, the difference between the ANIT-treated germfree and conventional groups was modest and most evident only within the first day following exposure. These findings suggest that the microbiome did not significantly affect ANIT-induced acute biliary tract injury in the conditions of this study.

Drug-induced Liver Fibrosis: Testing Nevirapine in a Viral-like Liver Setting Using Histopathology, MALDI IMS, and Gene Expression.

Nevirapine (NVP) is associated with hepatotoxicity in 1-5% of patients. In rodent studies, NVP has been shown to cause hepatic enzyme induction, centrilobular hypertrophy, and skin rash in various rat strains but not liver toxicity. In an effort to understand whether NVP is metabolized differently in a transiently inflamed liver and whether a heightened immune response alters NVP-induced hepatic responses, female brown Norway rats were dosed with either vehicle or NVP alone (75 mg/kg/day for 15 days) or galactosamine alone (single intraperitoneal [ip] injection on day 7 to mimic viral hepatitis) or a combination of NVP (75/100/150 mg/kg/day for 15 days) and galactosamine (single 750 mg/kg ip on day 7). Livers were collected at necropsy for histopathology, matrix-assisted laser desorption/ionization imaging mass spectrometry and gene expression. Eight days after galactosamine, hepatic fibrosis was noted in rats dosed with the combination of NVP and galactosamine. No fibrosis occurred with NVP alone or galactosamine alone. Gene expression data suggested a viral-like response initiated by galactosamine via RNA sensors leading to apoptosis, toll-like receptor, and dendritic cell responses. These were exacerbated by NVP-induced growth factor, retinol, apoptosis, and periostin effects. This finding supports clinical reports warning against exacerbation of fibrosis by NVP in patients with hepatitis C.

Utilization patterns for oral oncology medications in a specialty pharmacy cycle management program.

BACKGROUND: The cycle management program (CMP) was implemented in 2008 at a national specialty pharmacy with a focus on providing specialized counseling and monitoring for patients on select oral oncology medications. The program now includes nine medications: bexarotene, dasatinib, erlotinib, everolimus, nilotinib, pazopanib, sorafenib, sunitinib, and vorinostat. Patients receive frequent assessments to encourage adherence, identify adverse events, and track discontinuations through a pharmacist outreach at the initiation of therapy, day 10 and 20 of the first month, then monthly thereafter. The use of oral agents is increasing in cancer patients, shifting away from regimens exclusively involving intravenous chemotherapy. This offers advantages for patients in terms of convenience, but introduces risk as patients become more responsible for the administration and monitoring of the medications. PURPOSE: To evaluate utilization patterns of the oral oncology medications in the CMP including adverse event occurrence, medication discontinuations, and adherence markers. METHODS: This study is a retrospective review of patient-reported data from the CMP assessments completed in 2013. Data collected include adverse events and grades, adherence markers, and discontinuation rates. A total of 1163 assessments were reviewed from 557 patients. The assessments included in the analysis were the initial assessment, 10-day assessment, 20-day assessment, and the first monthly follow-up assessment, which encompasses the first two months of therapy. RESULTS: A total of 1453 adverse events were reported. Adverse events were cited as the reason for 39% of discontinuations and 28% of missed/held doses. A total of 101 discontinuations were reported across the nine CMP medications based on the first two months of data. Missed or held doses were reported in 130 assessments. CONCLUSIONS: Patient engagement and pharmacist interventions, through programs such as the CMP, are important to help patients manage these complex, high-risk medications.

Comedications alter drug-induced liver injury reporting frequency: Data mining in the WHO VigiBase™.

Polypharmacy is common, and may modify mechanisms of drug-induced liver injury. We examined the effect of these drug-drug interactions on liver safety reports of four drugs highly associated with hepatotoxicity. In the WHO VigiBase™, liver event reports were examined for acetaminophen, isoniazid, valproic acid, and amoxicillin/clavulanic acid. Then, we evaluated the liver event reporting frequency of these 4 drugs in the presence of co-reported medications. Each of the 4 primary drugs was reported as having more than 2000 liver events, and co-reported with more than 600 different medications. Overall, the effect of 2275 co-reported drugs (316 drug classes) on the reporting frequency was analyzed. Decreased liver event reporting frequency was associated with 245 drugs/122 drug classes, including anti-TNFα, opioids, and folic acid. Increased liver event reporting frequency was associated with 170 drugs/82 drug classes; in particular, halogenated hydrocarbons, carboxamides, and bile acid sequestrants. After adjusting for age, gender, and other co-reported drug classes, multiple co-reported drug classes were significantly associated with decreased/increased liver event reporting frequency in a drug-specific/unspecific manner. In conclusion, co-reported medications were associated with changes in the liver event reporting frequency of drugs commonly associated with hepatotoxicity, suggesting that comedications may modify drug hepatic safety.

Biliary proliferative lesions in the Sprague-Dawley rat: adverse/non-adverse.

Whether biliary proliferative lesions in nonclinical species are predictive of potential hepatotoxicity in humans depends, at least in part, on the nature and severity of such changes in the nonclinical species. We reviewed published literature (clinical and nonclinical) and experimental data from rat toxicology studies conducted by GlaxoSmithKline and the National Institute of Environmental Health Sciences' National Toxicology Program in an effort to better characterize the relative risk of hepatobiliary effects in humans. Available evidence supports the interpretation that minimal "typical" appearing bile duct hyperplasia limited to the portal triads may be considered non-adverse in the rat and is of little to no concern to humans. The toxicological relevance of mild to moderate "typical" hyperplasia is less certain, and may be considered adverse in the rat and potentially pose a risk for humans, particularly if accompanied by evidence of hepatobiliary injury or functional compromise. In addition, any proliferative lesion that includes atypical or dysplastic epithelial changes, oval cell proliferation, and/or significant extension beyond the portal tracts is considered more ominous and may be considered adverse in the rat.

Brief communication: intraperitoneal galactosamine misdosing as a possible interpretation for responder/nonresponder phenotypes.

Previous reports investigating the mechanisms of galactosamine toxicity have discussed the presence of responders and nonresponders after intraperitoneal (IP) administration of a toxic dose. The incidence of nonresponders has been reported to be as high as 47%. To rule out inadvertent intestinal, solid organ, or subcutaneous injection as at least a partial cause for the variability, we performed midline incisions and dosed 10 rats via a flexible catheter, with a toxic dose of galactosamine. Results were compared to a previous range finding study with IP-injected rats. As opposed to the IP-injected rats that had a roughly 50% response rate (based on serum alanine aminotransferase [ALT] elevation) and 100% of the midline incision catheter-instilled rats had elevations in ALT. Saline controls had no elevations. Histopathologic examination of livers from 5 midline-incisioned rats euthanized 48 hr after dosing with the lowest ALT responses revealed portal eosinophilic infiltrates and biliary hypertrophy/hyperplasia contiguous with areas of necrosis. Examination of 5 rats with the highest ALT elevations euthanized 10 days post dose revealed similar lesions to be resolving. We conclude that a significant contribution to variability in response to IP-injected galactosamine and possibly other investigative drugs is inadvertent misinjection of all or part of the dose.

Effects of Kupffer cell depletion on acute alpha-naphthylisothiocyanate-induced liver toxicity in male mice.

Depletion of Kupffer cells, known to modulate chemical-induced hepatocellular injury, has not been studied with regard to biliary epithelial injury. Here, the authors investigated the effect of Kupffer cell depletion by clodronate on the toxicity of alpha-naphthylisothiocyanate (ANIT), known to injure biliary epithelium as well as hepatocytes. Up to 99% depletion of Kupffer cells occurred in ANIT and liposome-encapsulated clodronate-treated mice. The effect of Kupffer cell depletion was most evident one day following ANIT treatment. Histologically, there was a modest increase in neutrophil infiltration of the bile ducts, hepatocytic necrosis, and microvesicular vacuolization in the ANIT and clodronate-treated mice, but differences between other groups did not persist. Clinical pathology analytes related to the biliary or hepatocellular injury were significantly elevated in ANIT and clodronate-treated mice compared to mice given clodronate only. This was also true for mice given ANIT and empty liposomes in the case of the biliary analytes. However, group means were typically higher for the ANIT and clodronate-treated group than others on the first 2 days following ANIT injection. These findings suggest that Kupffer cell reduction increases hepatobiliary damage due to ANIT treatment.

Lactic acidosis incidence with metformin in patients with type 2 diabetes and chronic kidney disease: A retrospective nested case-control study.

Objective: Compare rates of lactic acidosis (LA) among metformin-exposed and unexposed patients with type 2 diabetes mellitus and varying degrees of chronic kidney disease (CKD). Research Design and Methods: Retrospective, nested case-control study using data from national VA Corporate Data Warehouse. All adult patients with type 2 diabetes and CKD newly dispensed any antihyperglycaemic medication during FY 2003-13 were included. The outcome was LA hospitalization or serum lactate >5 mEq/L. Exposure to metformin was evaluated in the three months prior to event. Estimates were adjusted for 31 covariates, including demographics, comorbidities and medications. Results: Overall, 320 882 patients were included, contributing a total of 1 331 784 person-years of follow-up. LA occurred in 2 665 patients, generating an overall incidence rate of 2.00 (95% CI 1.93-2.08) per 1000 person-years. Metformin exposure in the prior 3 months was associated with an elevated adjusted hazard of LA (HR 1.97, 95% CI 1.69-2.29). No association was evident in patients with CKD stage 1 or 2 (HR 1.05, 95% CI 0.71-1.57), but associations were present and progressively greater in patients with CKD stage 3a through 5: HR 3.09, 95% CI 2.19-4.35 in CKD 3a, HR 3.34, 95% CI 1.95-5.72 in CKD 3b, HR 7.87, 95% CI 3.51-17.61 in CKD stage 4&5. Conclusion: Metformin was not associated with an elevated risk of LA in persons with stage 1-2 CKD, but was associated with a progressively higher risk at more advanced stages of CKD.

Estimated Cost and Savings in a Patient Management Program for Oral Oncology Medications: Impact of a Split-Fill Component.

PURPOSE: A national specialty pharmacy implemented a split-fill option within an oral oncology patient management program to reduce pharmacy costs and medication wastage resulting from early discontinuations. Payers covered dispensed medications at half-quantity intervals for each dispense up to 3 months. Proactive outreach to patients before they had used up the initial dispensed medication quantity helped assess the patient's tolerance to the new medication and adverse effects. This study compared costs for patients with a split-fill option to similar costs for patients without this option taking into account patient discontinuation rates, patient-reported adverse effects rates, estimated pharmacy costs, and potential wastage. METHODS: This retrospective cohort study included patients who were new to therapy on a split-fill medication between September 2015 and August 2017. A 1:1 greedy match algorithm was conducted using propensity variables to match patients from each cohort. Per-month discontinuation rates were determined for both split-fill and non-split-fill groups. The non-split-fill potential wastage was calculated as monthly costs for discontinuations in the following month and weighted by split-fill discontinuation rates. RESULTS: Of the 2,363 program patients who met selection criteria for the 11 medications, 671 patients from each group were matched. Payers with a split-fill program had significant medication savings per covered month ($2,147.60 at 1 month) and at a cumulative 6 months. Modeled wastage indicated that payers without a split-fill program could expect to save $2,646.74 monthly by using this option. Both cohorts had similar rates of adverse effects and time until first reported adverse effect. CONCLUSION: In the first 6 months, the split-fill patient managed program had lower discontinuation rates, significantly reduced pharmacy costs, and reduced potential wastage.

Retrospective Analysis of Medication Utilization and Clinical Outcomes in Patients With Idiopathic Pulmonary Fibrosis Treated With Nintedanib or Pirfenidone.

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease which results in thickening and scarring of the interstitial tissue. As the only 2 Food and Drug Administration (FDA)-approved medications on the market, it is valuable to compare the impact of nintedanib and pirfenidone on clinical outcomes. Records of patients who started nintedanib or pirfenidone between calendar years 2015 and 2016 at a national specialty pharmacy were retrospectively reviewed. Data collection was derived from patient management applications and statistical data analysis was completed in SAS (SAS Institute Inc®). The nintedanib population contained 2605 patients and of the population completing clinical assessment surveys (n = 1343), 46% of respondents (n = 612) reported no adverse events, with the remaining 54% reporting at least 1 adverse event. Average proportion of days covered (PDC) was 84.2% (SD = 17.0). Average final monthly copay for this group was $235. The pirfenidone population had 1322 patients, and of the surveyed population (n = 764), 58% of respondents (n = 445) reported no adverse events, with the remaining 42% reporting at least 1 adverse event. Average PDC was 83.4% (SD = 17.3). Average final monthly copay for this group was $339. Outcomes in the studied IPF population were similar for nintedanib and pirfenidone.

Retrospective Analysis of the Medication Utilization and Clinical Outcomes of Patients Treated with Various Regimens for Hepatitis C Infection.

BACKGROUND: The hepatitis C virus (HCV) is the most common chronic blood-borne infection and the leading cause of liver transplantation in the United States. There are approximately 3.2 million people currently infected with HCV in the United States. In late 2013, the introduction of sofosbuvir and simeprevir represented a critical advancement in the treatment of HCV by improving sustained virologic response (SVR) rates. PURPOSE: The purpose of this study was to evaluate medication utilization and clinical outcomes of patients with HCV who were treated with any Food and Drug Administration-approved combination of ribavirin, peginterferon products, simeprevir, and sofosbuvir. METHODS: Prescription records and clinical assessment forms of patients who started HCV therapy and were eligible for SVR between January 1, 2014, and December 31, 2014, were retrospectively reviewed. Data collection included patient demographics, genotype, SVR, patient-reported adverse events, discontinuations, and adherence markers. RESULTS: A total of 367 eligible patients were identified who had initiated treatment during the study period. Genotype 1 was the most common genotype, and an overall SVR rate of 86.9% was observed. Results were similar to those seen in phase III clinical trials. In addition, adverse events of these medications were more tolerable, and discontinuation rates were lower than with previous therapies.

The role of pathology in the identification of drug-induced hepatic toxicity.

Pathologists play a central role in the recognition and prevention of drug-induced toxicity. Pathologists engaged in clinical practice must identify a pattern of histological lesions that are interpreted in concert with a variety of clinical data to determine the probability of drug-induced toxicity versus background disease processes and the most likely drug, often of many, to have caused the specific injury. Toxicological pathologists, working in concert with other scientists, have the responsibility of preventing drug-induced toxicity in humans by identifying potentially toxic drugs and keeping them from the marketplace. In this process of drug development, a broad array of in vivo testing using a number of animal species and in vitro assays are used. Technological advances require pathologists to integrate molecular-based mechanistic data effectively with traditional morphological evaluation to develop a more detailed grasp of the pathogenesis of drug-induced injury. All pathologists have the responsibility to effectively and accurately communicate their findings and interpretations to the appropriate audiences.

Gene expression profiling of the PPAR-alpha agonist ciprofibrate in the cynomolgus monkey liver.

Fibrates, such as ciprofibrate, fenofibrate, and clofibrate, are peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists that have been in clinical use for many decades for treatment of dyslipidemia. When mice and rats are given PPARalpha agonists, these drugs cause hepatic peroxisome proliferation, hypertrophy, hyperplasia, and eventually hepatocarcinogenesis. Importantly, primates are relatively refractory to these effects; however, the mechanisms for the species differences are not clearly understood. Cynomolgus monkeys were exposed to ciprofibrate at various dose levels for either 4 or 15 days, and the liver transcriptional profiles were examined using Affymetrix human GeneChips. Strong upregulation of many genes relating to fatty acid metabolism and mitochondrial oxidative phosphorylation was observed; this reflects the known pharmacology and activity of the fibrates. In addition, (1) many genes related to ribosome and proteasome biosynthesis were upregulated, (2) a large number of genes downregulated were in the complement and coagulation cascades, (3) a number of key regulatory genes, including members of the JUN, MYC, and NFkappaB families were downregulated, which appears to be in contrast to the rodent, where JUN and MYC are reported to upregulated after PPARalpha agonist treatment, (4) no transcriptional signal for DNA damage or oxidative stress was observed, and (5) transcriptional signals consistent with an anti-proliferative and a pro-apoptotic effect were seen. We also compared the primate data to literature reports of hepatic transcriptional profiling in PPARalpha-treated rodents, which showed that the magnitude of induction in beta-oxidation pathways was substantially greater in the rodent than the primate.

Opposing mechanisms of NADPH-cytochrome P450 oxidoreductase regulation by peroxisome proliferators.

Peroxisome proliferators (PPs) regulate a battery of rodent P450 genes, including CYP2B, CYP2C, and CYP4A family members. We hypothesized that other components of the P450-metabolizing system are altered by exposure to PPs, including NADPH-cytochrome P450 oxidoreductase (P450R), an often rate-limiting component in P450-dependent reactions. In this study, we determined whether exposure to structurally diverse PPs alters the expression of P450R mRNA and protein. Increases in P450R mRNA levels were observed in male and female F-344 rat livers and in male rat kidneys after chronic exposure of the animals to PPs. Paradoxically, under the same treatment conditions in male rats, liver P450R protein levels decreased after exposure to the PPs Wy-14,643 ([4-chloro-6-(2,3-xylidino)pyrimidynylthio]acetic acid) (WY) or gemfibrozil (GEM). The down-regulation of the P450R protein was sex- and tissue-specific in that exposure to PPs led to increases in P450R protein in female rat livers [di-n-butyl phthalate (DBP) only] and male rat kidneys (WY, GEM, DBP). In male wild-type SV129 mice, P450R mRNA levels increased in livers after exposure to WY and diethylhexyl phthalate (DEHP) and in male kidneys after exposure to DEHP. Induction of mRNA by PPs was not observed in the liver or kidneys of mice, which lack a functional peroxisome proliferator-activated receptor alpha (PPAR alpha), the central mediator of the effects of PPs in the rodent liver. In wild-type male mice, P450R protein was decreased in liver after WY and DEHP treatment and in kidneys after WY treatment. The down-regulation of the P450R protein was not observed in PPAR alpha-null mice. These studies demonstrate the complex regulation of P450R expression by PPs at two different levels, both of which are dependent upon PPAR alpha: up-regulation of transcript levels in liver and kidneys and down-regulation of protein levels in male rat and mouse liver by a novel posttranscriptional mechanism.

Development of a community residency program with a focus on specialty pharmacy.

PURPOSE: An innovative community residency program that provides training in the clinical and administrative aspects of specialty pharmacy practice is described. SUMMARY: An ongoing rapid rise in U.S. approvals of specialty therapies for chronic diseases and conditions (e.g., Crohn's disease, cystic fibrosis, infertility, hepatitis C infection, multiple sclerosis) is fueling demand for pharmacists trained to meet the complex needs of patients receiving those therapies, which are typically subject to risk evaluation and mitigation strategy (REMS) requirements and limited distribution arrangements. In 2011, Duquesne University Mylan School of Pharmacy partnered with Walgreens Specialty Pharmacy to launch a one-year community residency program designed to (1) provide enhanced education on diseases and conditions targeted by specialty therapies, (2) develop well-rounded clinicians who are fully knowledgeable of the medications used to treat those disorders, and (3) prepare trainees for the operational and business-related challenges of specialty pharmacy practice. The first half of the residency year emphasizes direct patient care experiences, with team-based rotations focusing on specific disease states and health conditions; the second half of the residency program emphasizes operational-administrative training in areas such as clinical program development, resource utilization review, REMS compliance, contracting, and navigating manufacturer-sponsored patient assistance programs. Other program components include a one-month external rotation at a managed care organization, research projects, and teaching experiences. CONCLUSION: A unique community residency program jointly developed by Duquesne University and Walgreens Specialty Pharmacy prepares trainees for careers in diverse clinical, managed care, community-based, and academic practice settings.

DINITROBENZENES STIMULATE ELECTRON FLUX WITHIN NEURONAL NITRIC OXIDE SYNTHASE IN THE ABSENCE OF CALMODULIN.

Efficient electron transfer and conversion of L-arginine to L-citrulline and nitric oxide (NO•) by neuronal nitric oxide synthase (nNOS) requires calmodulin (CaM) binding. The present study focused on electron transfer ability of resting state CaM-free nNOS in presence of dinitrobenzene isomers (DNBs). NADPH oxidation (NADPH ox ) and acetylated cytochrome-c reduction (AcCyt-cred ) catalyzed by nNOS and the CaM binding sequence-deficient nNOS reductase construct (nNOS-FP) were estimates of total electron flux and [Formula: see text] production, respectively. All the DNBs (o-, m-, p-) independently stimulated rates of NADPH ox by CaM-free nNOS and by nNOS-FP in isomer- and concentration-dependent manner. Blocking nNOS heme by imidazole or L-arginine did not affect CaM-free nNOS-catalyzed NADPH ox stimulated by DNBs. This stimulated electron flux by DNBs did not support NO• formation by CaM-free nNOS. The DNBs, like FeCN, extract electrons from both FMN and FAD of the nNOS reductase domain. All three DNBs greatly stimulated nNOS and nNOS-FP catalyzed AcCyt-cred that was significantly inhibited by SOD demonstrating [Formula: see text] formation. Thus, in presence of DNBs, resting-state CaM-deficient nNOS efficiently transfers electrons generating [Formula: see text], inferring that additional metabolic roles for nNOS exist that are not yet explored.