Evaluation of a Live-Attenuated Human Parainfluenza Type 1 Vaccine in Adults and Children

We conducted a phase I clinical trial (clinicaltrials.gov identifier, NCT00641017) of the experimental live-attenuated human parainfluenza virus type 1 (HPIV-1) vaccine rHPIV-1/84/del 170/942A sequentially in 3 groups: adults, HPIV-1-seropositive children, and HPIV-1-seronegative children, the target population for vaccination. rHPIV-1/84/del 170/942A was appropriately restricted in replication in adults and HPIV-1-seropositive children but was overattenuated (ie, insufficiently infectious and immunogenic) for HPIV-1-seronegative children.

Human parainfluenza virus serotypes differ in their kinetics of replication and cytokine secretion in human tracheobronchial airway epithelium

Human parainfluenza viruses (PIVs) cause acute respiratory illness in children, the elderly, and immunocompromised patients. PIV3 is a common cause of bronchiolitis and pneumonia, whereas PIV1 and 2 are frequent causes of upper respiratory tract illness and croup. To assess how PIV1, 2, and 3 differ with regard to replication and induction of type I interferons, interleukin-6, and relevant chemokines, we infected primary human airway epithelium (HAE) cultures from the same tissue donors and examined replication kinetics and cytokine secretion. PIV1 replicated to high titer yet did not induce cytokine secretion until late in infection, while PIV2 replicated less efficiently but induced an early cytokine peak. PIV3 replicated to high titer but induced a slower rise in cytokine secretion. The T cell chemoattractants CXCL10 and CXCL11 were the most abundant chemokines induced. Differences in replication and cytokine secretion might explain some of the differences in PIV serotype-specific pathogenesis and epidemiology.

Progress in the development of human parainfluenza virus vaccines

In children under 5 years of age, human parainfluenza viruses (HPIVs) as a group are the second most common etiology of acute respiratory illness leading to hospitalization, surpassed only by respiratory syncytial virus but ahead of influenza viruses. Using reverse genetics systems for HPIV serotypes 1, 2 and 3 (HPIV1, 2 and 3), several live-attenuated HPIVs have been generated and evaluated as intranasal vaccines in adults and in children. Two vaccines against HPIV3 were found to be well tolerated, infectious and immunogenic in Phase I trials in HPIV3-seronegative infants and children and should progress to proof-of-concept trials. Vaccines against HPIV1 and HPIV2 are less advanced and have just entered pediatric trials.

Epstein-Barr virus genetics: talking about the BAC generation

Genetic mutant organisms pervade all areas of Biology. Early on, herpesviruses (HV) were found to be amenable to genetic analysis using homologous recombination techniques in eukaryotic cells. More recently, HV genomes cloned onto a bacterial artificial chromosome (BAC) have become available. HV BACs can be easily modified in E.coli and reintroduced in eukaryotic cells to produce infectious viruses. Mutants derived from HV BACs have been used both to understand the functions of all types of genetic elements present on the virus genome, but also to generate mutants with potentially medically relevant properties such as preventative vaccines. Here we retrace the development of the BAC technology applied to the Epstein-Barr virus (EBV) and review the strategies available for the construction of mutants. We expand on the appropriate controls required for proper use of the EBV BACs, and on the technical hurdles researchers face in working with these recombinants. We then discuss how further technological developments might successfully overcome these difficulties. Finally, we catalog the EBV BAC mutants that are currently available and illustrate their contributions to the field using a few representative examples.

A novel human parainfluenza virus type 1 (HPIV1) with separated P and C genes is useful for generating C gene mutants for evaluation as live-attenuated virus vaccine candidates

A novel recombinant human parainfluenza virus type 1 (rHPIV1), rHPIV1-C+P, in which the overlapping open reading frames of the C and P genes were separated in order to introduce mutations into the C gene without affecting P, was generated. Infectious rHPIV1-C+P was readily recovered and replicated as efficiently as HPIV1 wild type (wt) in vitro and in African green monkeys (AGMs). rHPIV1-C+P expressed increased levels of C protein and, surprisingly, activated the type I IFN and apoptosis responses more strongly than HPIV1 wt. rHPIV1-C+P provided a useful backbone for recovering an attenuated P/C gene mutation (Delta 84-85), which was previously unrecoverable, likely due to detrimental effects of the deletion on the P protein. rHPIV1-C(Delta 84-85)+P and an additional mutant, rHPIV1-C(Delta 169-170)+P, were found to replicate to similar titers in vitro and to activate the type I IFN and apoptosis responses to a similar degree as rHPIV1-C+P. rHPIV1-C(Delta 84-85)+P was found to be highly attenuated in AGMs, and all viruses were immunogenic and effective in protecting AGMs against challenge with HPIV1 wt. rHPIV1-C(Delta 84-85)+P will be investigated as a potential live-attenuated vaccine candidate for HPIV1.

Role of interferon in the replication of human parainfluenza virus type 1 wild type and mutant viruses in human ciliated airway epithelium

Human parainfluenza virus type 1 (HPIV1) is a significant cause of pediatric respiratory disease in the upper and lower airways. An in vitro model of human ciliated airway epithelium (HAE), a useful tool for studying respiratory virus-host interactions, was used in this study to show that HPIV1 selectively infects ciliated cells within the HAE and that progeny virus is released from the apical surface with little apparent gross cytopathology. In HAE, type I interferon (IFN) is induced following infection with an HPIV1 mutant expressing defective C proteins with an F170S amino acid substitution, rHPIV1-C(F170S), but not following infection with wild-type HPIV1. IFN induction coincided with a 100- to 1,000-fold reduction in virus titer, supporting the hypothesis that the HPIV1 C proteins are critical for the inhibition of the innate immune response. Two recently characterized live attenuated HPIV1 vaccine candidates expressing mutant C proteins were also evaluated in HAE. The vaccine candidates, rHPIV1-C(R84G/Delta170)HN(T553A)L(Y942A) and rHPIV1-C(R84G/Delta170)HN(T553A)L(Delta1710-11), which contain temperature-sensitive (ts) attenuating (att) and non-ts att mutations, were highly restricted in growth in HAE at permissive (32 degrees C) and restrictive (37 degrees C) temperatures. The viruses grew slightly better at 37 degrees C than at 32 degrees C, and rHPIV1-C(R84G/Delta170)HN(T553A)L(Y942A) was less attenuated than rHPIV1-C(R84G/Delta170)HN(T553A)L(Delta1710-11). The level of replication in HAE correlated with that previously observed for African green monkeys, suggesting that the HAE model has potential as a tool for the preclinical evaluation of HPIV1 vaccines, although how these in vitro data will correlate with vaccine virus replication in seronegative human subjects remains to be seen.

Attenuation and efficacy of human parainfluenza virus type 1 (HPIV1) vaccine candidates containing stabilized mutations in the P/C and L genes

Background

Two recombinant, live attenuated human parainfluenza virus type 1 (rHPIV1) mutant viruses have been developed, using a reverse genetics system, for evaluation as potential intranasal vaccine candidates. These rHPIV1 vaccine candidates have two non-temperature sensitive (non-ts) attenuating (att) mutations primarily in the P/C gene, namely C^R84GHN^T553A (two point mutations used together as a set) and C^Δ170 (a short deletion mutation), and two ts att mutations in the L gene, namely L^Y942A (a point mutation), and L^Δ1710–11 (a short deletion), the last of which has not been previously described. The latter three mutations were specifically designed for increased genetic and phenotypic stability. These mutations were evaluated on the HPIV1 backbone, both individually and in combination, for attenuation, immunogenicity, and protective efficacy in African green monkeys (AGMs).

Results

The rHPIV1 mutant bearing the novel L^Δ1710–11 mutation was highly ts and attenuated in AGMs and was immunogenic and efficacious against HPIV1 wt challenge. The rHPIV1-C^R84G/Δ170HN^T553AL^Y942A and rHPIV1-C^R84G/Δ170HN^T553AL^Δ1710–11 vaccine candidates were highly ts, with shut-off temperatures of 38°C and 35°C, respectively, and were highly attenuated in AGMs. Immunization with rHPIV1-C^R84G/Δ170HN^T553AL^Y942A protected against HPIV1 wt challenge in both the upper and lower respiratory tracts. In contrast, rHPIV1-C^R84G/Δ170HN^T553AL^Δ1710–11 was not protective in AGMs due to over-attenuation, but it is expected to replicate more efficiently and be more immunogenic in the natural human host.

Conclusion

The rHPIV1-C^R84G/Δ170HN^T553AL^Y942A and rHPIV1-C^R84G/Δ170HN^T553AL^Δ1710–11 vaccine candidates are clearly highly attenuated in AGMs and clinical trials are planned to address safety and immunogenicity in humans.

Differential activities of alpha/beta IFN subtypes against influenza virus in vivo and enhancement of specific immune responses in DNA vaccinated mice expressing haemagglutinin and nucleoprotein

Vaccines are urgently needed to elicit immunity to different influenza virus strains. DNA vaccines can elicit partial protective immunity, however their efficacy requires improvement. We assessed the capacity of individual type I IFN multigene family members as subtype transgenes to abrogate influenza virus replication in a vaccination/challenge mouse model. Differences in antiviral efficacy were found among the subtypes with IFNA5 and IFNA6 being most effective, while IFNA1 was the least effective in reducing lung virus replication. Mice vaccinated with combinatorial HA/IFNA6 or NP/IFNA6 showed reduced lung viral titres, clinical score, body weight loss, and pulmonary tissue damage compared to IFNA6, HA, or NP viral vaccination alone. In addition, IFNA6 increased IgG2a titres with upregulation of IFN-gamma response in the respiratory tract. We conclude that IFN-alpha 6 has antiviral and immunomodulatory effects, which improve efficacy of DNA vaccines for enhanced control of influenza.

Attenuating mutations in the P/C gene of human parainfluenza virus type 1 (HPIV1) vaccine candidates abrogate the inhibition of both induction and signaling of type I interferon (IFN) by wild-type HPIV1

Recombinant human parainfluenza virus type 1 (HPIV1) and mutants containing point and deletion (Delta) mutations in the P/C gene (r-CDelta10-15HNT553A, r-CR84G, r-CF170S and r-CDelta170), which have previously been evaluated as HPIV1 vaccine candidates, were evaluated for their effect on the type I interferon (IFN) response in vitro. HPIV1 wt infection inhibited the IFN response by inhibiting IFN regulatory factor-3 (IRF-3) activation and IFN production in A549 cells and IFN signaling in Vero cells. In contrast, r-CR84G, r-CF170S and r-CDelta170 were defective for inhibition of IRF-3 activation and IFN production and r-CF170S and r-CDelta170 did not inhibit IFN signaling. Thus, HPIV1 antagonizes the IFN response at both the level of induction and signaling, and antagonism at both levels was disrupted by mutations in the P/C gene. Because CF170S affects C and not P, the anti-IFN function can be attributed to the C proteins. These data, in the context of previous in vivo studies, suggest that the loss of antagonism of the IFN response at both the level of induction and signaling, observed with the P/C mutants, r-CF170S and r-CDelta170, was necessary for significant attenuation in African green monkeys (AGMs).

Introducing point and deletion mutations into the P/C gene of human parainfluenza virus type 1 (HPIV1) by reverse genetics generates attenuated and efficacious vaccine candidates

The P/C gene of human parainfluenza virus type 1 (HPIV1) encodes a nested set of related accessory C proteins, C'/C/Y1/Y2, which have been shown in other paramyxoviruses to have a role in evasion of the type I interferon (IFN) response following virus infection. We previously demonstrated that a set of two amino acid substitutions, CR84G/HNT553A, and a separate amino acid substitution, CF170S, are independently attenuating for HPIV1 in African green monkeys (AGMs). However, in each case the attenuation (att) phenotype is vulnerable to reversion by a single nucleotide change back to wild type. Using reverse genetics, recombinant HPIV1 (rHPIV1) vaccine candidates were generated that were designed for increased genetic and phenotypic stability by: (i) creating a two-amino acid deletion and substitution at the site of the CF170S mutation, yielding CDelta170; (ii) introducing a six amino acid deletion in the N-terminal region of C, CDelta10-15; and (iii) combining these stable deletion mutations with the att CR84G/HNT553A mutation. The resulting rHPIV1 vaccine candidates were evaluated for attenuation in hamsters and AGMs and for immunogenicity and protective efficacy in AGMs. The CDelta10-15 mutation was attenuating in hamsters but not in AGMs, and likely will be of limited value for an HPIV1 vaccine. Conversely, the CR84G/HNT553A mutation set was attenuating in AGMs but not in hamsters. Thus, these two mutations demonstrated reciprocal host range phenotypes involving different regions of C. The CDelta170 mutation conferred a significant level of attenuation in hamsters and AGMs that closely resembled that of CF170S and will be of particular utility for vaccine development because it involves a deletion of six nucleotides rendering it highly refractory to reversion. The combination of the CR84G/HNT553A mutation set and the CDelta170 deletion mutation yielded a virus, rCR84G/Delta170 HNT553A, that exhibited a satisfactory level of attenuation in hamsters and AGMs and was immunogenic and highly protective against HPIV1 wt challenge. This virus will be evaluated clinically as a live intranasal HPIV1 vaccine, one that can be further attenuated as necessary by the introduction of additional stabilized att mutations previously developed in the L protein.

Human parainfluenza virus type I (HPIV1) vaccine candidates designed by reverse genetics are attenuated and efficacious in African green monkeys

A set of recombinant, live attenuated human parainfluenza virus type 1 (rHPIV1) vaccine candidates was evaluated for attenuation, immunogenicity, and protective efficacy in African green monkeys (AGMs). Temperature sensitive (ts) and non-ts attenuating (att) mutations in the P/C and L genes were introduced individually or in various combinations into rHPIV1, including the C(R84G) and HN(T553A) mutations identified in the present work and the C(F170S), L(Y942A), and L(L992C) mutations identified previously. The rHPIV1 vaccine candidates exhibited a spectrum of attenuation in AGMs. One genetically and phenotypically stable vaccine candidate, rC(R84G/F170S)L(Y942A/L992C), was attenuated and efficacious in AGMs and is a promising live attenuated intranasal HPIV1 vaccine candidate suitable for clinical evaluation.

Interferon subtype gene therapy for regulating cytomegalovirus disease

Delivery of type I interferon (IFN) subtypes by intramuscular inoculation of mice with a recombinant mammalian expression vector encoding IFN stimulates the immune response. Such immunomodulation drives towards a Th1-like response. The degree of stimulation of the immune response was influenced by several parameters of the naked deoxyribonucleic acid (DNA) vaccination protocol. Pretreatment of mice with bupivacaine increased transgene expression in situ. The specific subtype gene of type I IFN, the DNA concentration, the combined use of two or more subtypes, and the timing of the DNA immunisations were all found to influence the level of efficacy of IFN gene therapy in a mouse model for cytomegalovirus (CMV) infection and disease. In addition, adjuvant therapy, using type I IFN genes, for DNA virus vaccination (CMV glycoprotein B) enhanced viral-specific immunity and reduced the severity of myocarditis in mice. Thus, type I IFN gene therapy has potent adjuvant properties when delivered as DNA and can be used to regulate virus infection and disease via pleiotropic actions in the stimulation of immune responses.

Type I IFN-beta gene therapy suppresses cardiac CD8+ T-cell infiltration during autoimmune myocarditis

Gene therapy using DNA encoding type I IFN subtypes IFNA6, IFNA9 and IFNB suppresses murine cytomegalovirus (MCMV)-myocarditis, a predominantly cell-mediated disease in BALB/c mice. CD8(+) T cells are the principal cell type within the inflamed myocardium. As such, we investigated the effects of IFN subtype treatment on this T-cell subset and other cell types in the cardiac infiltrate. In the acute phase of disease, IFNA6 and IFNA9 treatments significantly reduced the number of CD8(+) T cells within the foci of cellular infiltration in the heart. During the chronic phase, which is primarily autoimmune in nature, IFNB treatment significantly reduced CD8(+) T cells. B-cell and neutrophil numbers in the cardiac infiltrate were also reduced following IFNB immunotherapy. Although early inflammatory responses are important for resolution of virus infection, high numbers of lymphocytes persisting in the myocardium may lead to exacerbation of disease. Our data suggests that type I IFN DNA therapy regulates cardiac cellular infiltration. Thus, treatment with IFN-beta administered prophylactically to high-risk patients in acquiring CMV infection may reduce the development of chronic autoimmune myocarditis.

Type I interferon differential therapy for erythroleukemia: specificity of STAT activation

Type I interferons (IFNs), pleiotropic cytokines with antiviral, antiproliferative, apoptotic, and immunoregulatory functions, are efficacious in the treatment of malignancies, viral infections, and autoimmune diseases. Binding of these cytokines to their cognate receptor leads to activation of the Jak-signal transducers and activators of transcription (STAT) signaling pathway and altered gene expression. This signal pathway has been intensely studied using human IFN-alpha 2 and IFN-beta. However, there are over 14 human IFN-alpha subtypes and over 10 murine IFN-alpha subtypes, with a single IFN-beta subtype in both species. J2E cells are immortalized at the proerythroblast stage of development and produce a rapid and fatal erythroleukemia in vivo. These cells retain the ability to respond to erythropoietin in vitro by proliferating, differentiating, and remaining viable in the absence of serum. Here, we show that J2E cells are also functionally regulated differentially by IFN subtype treatment in vitro. A novel finding was the selective activation of STAT and mitogen-activated protein kinase (MAPK) molecules by different subtypes binding the IFN receptor. These findings indicate distinct effects for individual type I IFN subtypes, which are able to differentially activate members of the STAT and MAPK family. Finally, we investigated the efficacy of IFN naked DNA therapy in treating J2E-induced erythroleukemia in athymic nude mice. IFN subtypes differentially regulated the onset of erythroleukemia with delayed onset and increased survival, possibly via a reduction in cell viability, and enhanced antiproliferative and apoptotic effects observed for IFNA6 and IFNA9 treatment, respectively. Moreover, these data highlight the necessity to choose the best IFN subtype in disease treatment.

Optimization of Naked DNA Delivery for Interferon Subtype Immunotherapy in Cytomegalovirus Infection

Type I interferon (IFN) gene therapy modulates the immune response leading to inflammatory heart disease following cytomegalovirus (CMV) infection in a murine model of post-viral myocarditis. Efficacy of different immunisation protocols for the IFN constructs was influenced by the dose of DNA, subtype choice, combination use, pre-medication, and timing of DNA administration. Optimal efficacy was found with bupivacaine treatment prior to DNA inoculation of 200mg IFN DNA 14 days prior to virus challenge. Maximal antiviral and antimyocarditic effects were achieved with this vaccination schedule. Furthermore, inoculation of synergistic IFN subtypes demonstrated enhanced efficacy when delivered either alone or with CMV gB DNA vaccination in the CMV model. Thus naked DNA delivery of IFN provides an avenue of immunotherapy for regulating herpesvirus-induced diseases.

Coimmunisation with type I IFN genes enhances protective immunity against cytomegalovirus and myocarditis in gB DNA-vaccinated mice

Viral DNA vaccines encoding the glycoprotein B (gB) of cytomegalovirus provide partial protective immunity upon challenge with infectious virus. Although it is known that type I IFN can stimulate the adaptive immune response, their direct use in vaccines has been limited. Here we show that coimmunisation of type I IFN and gB CMV DNA constructs enhances protective immunity in mice. In vivo expression of IFN transgenes ranged from 1.2 to 2.0 x 10(4) IU/g tibialis anterior muscle. Viral titre in major target organs and the severity of acute CMV-induced myocarditis was reduced preferentially with either IFN-alpha 9 or IFN-beta, but not with IFN-alpha 6, coimmunisation. However, all IFN subtypes investigated markedly reduced chronic myocarditis in gB-vaccinated mice. The early antiviral IgG1 and IgG2a titres were enhanced with IFN-beta coimmunisation. TNF and IL-10 was increased in response to MCMV infection in mice coimmunised with IFN subtypes and viral gB DNA. Indeed T cells from IFN-inoculated mice reduced myocarditis upon in vivo transfer. These results suggest that select type I IFNs may act as a natural adjuvant for the immune response against CMV infection. Type I IFN DNA coimmunisation may provide increased efficacy for viral vaccines and subsequently modulate post-viral chronic inflammatory disorders.

Synergy of type I interferon-A6 and interferon-B naked DNA immunotherapy for cytomegalovirus infection

Delivery of type I IFN transgenes by naked DNA immunization can protect against cytomegalovirus infection and myocarditis. Here, we investigate IFN transgene expression, antiviral efficacy, and immunomodulation of myocarditis using various treatment regimes in a mouse CMV model. In vivo expression of the IFN transgene was observed in the sera for 35 days post-DNA inoculation. Prophylactic IFN-A6 and IFN-B DNA treatment for 14 days prior to murine cytomegalovirus (MCMV) infection was more efficacious in significantly reducing viral titres, than 2 days prior to or 2 days post-virus infection. Similarly, IFN-A6 DNA treatment commencing 14 days prior to virus infection was superior in suppressing both acute and chronic myocarditis. Furthermore, reduction of autoantibody titres was more pronounced when IFN was administered 14 days prior to viral infection. Combinational IFN gene therapy was assessed for synergy between IFN subtypes. Combination treatment with either IFN-A6/A9 or IFN-A6/B greatly reduced spleen viral titres while IFN-A6/B and IFN-A9/B reduced virus replication in the liver. Only IFN-A6/A9 and IFN-A9/B reduced acute viral myocarditis, whereas IFNA6/B treatment was most efficacious for autoimmune chronic myocarditis. Finally, treatment with IFN-A6 DNA 2 weeks post-MCMV infection proved effective at inhibiting the development of chronic autoimmune myocarditis. These findings suggest that immunomodulation of both antiviral and autoimmune responses by IFN DNA immunization may be an avenue for improved viral immunotherapy.

Type I interferon gene therapy protects against cytomegalovirus-induced myocarditis

Type I interferons (IFNs) are produced early in response to viral infection and modulate adaptive immunity. Previously we demonstrated localized protection against murine cytomegalovirus (MCMV) infection in IFN DNA-inoculated mice. Here we examine the effect of seven IFN subtypes (IFNA1, A2, A4, A5, A6, A9 and B), administered by DNA inoculation, on systemic MCMV infection and myocarditis. IFN transgene expression altered the pathogenesis of MCMV infection with regard to virus titre and myocarditis. IFNA6 treatment reduced MCMV replication whilst IFNA5 and A2 enhanced virus replication. IFNA6, A9, and B treatment inhibited acute myocarditis. A T helper type 1-like, antibody and cytokine, response correlated with decreased virus titre and myocarditis. In addition, IFNA6 was able to reduce chronic cardiac inflammation. This research into the effectiveness of seven type I IFNs, using DNA gene therapy, highlights the need for correct subtype usage in the treatment of disease. We demonstrate effective subtypes for treatment in both the acute and chronic phases of MCMV infection and the resultant development of myocarditis.

Effect of a haloperidol challenge on regional brain metabolism in neuroleptic-responsive and nonresponsive schizophrenic patients

OBJECTIVE

The CNS metabolic response to a neuroleptic challenge in treatment-responsive and nonresponsive schizophrenic patients was measured in order to examine the relation between treatment outcome and the capacity to alter neurochemical function in response to acute receptor blockade.

METHOD

Positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG) were used to measure regional cerebral metabolism in seven schizophrenic patients judged to have been responsive to drug treatment previously and seven nonresponsive schizophrenic patients after a drug-free period of at least 3 weeks (baseline) and again 12 hours after administration of 5.0 mg of haloperidol.

RESULTS

The haloperidol challenge caused widespread decreases in absolute metabolism in the nonresponsive patients but not the responsive patients. These group differences reflect the findings on the second (challenge) scans, since metabolic values at baseline were not statistically different in the two groups. The pattern of decreased metabolic activity in the nonresponders after the haloperidol challenge is similar to that previously observed in normal subjects.

CONCLUSIONS

The metabolic response to drug challenge separates treatment responders from nonresponders and normal subjects. The results suggest that subtyping of schizophrenia (and other psychiatric disorders) can be achieved by measuring the physiologic response to a pharmacologic challenge in vivo with chemical brain-imaging techniques.

The study of neurotransmitter interactions using positron emission tomography and functional coupling

Functional brain imaging with positron emission tomography (PET) has opened up new avenues for the investigation of possible functional disturbances related to psychiatric disease as well as pharmacodynamic assessment of drug treatment in vivo. Different strategies to study pharmacologic effects on the brain have been developed in recent years. The basic methods are to measure (a) blood flow or glucose metabolism, (b) parameters of specific receptor binding, or (c) neurotransmitter metabolism. Each of these can be performed either in a resting state or after perturbation with a pharmacologic challenge. Our group has developed a general strategy for investigating pharmacologic effects on brain function: (a) determining indirect drug-induced metabolic changes with fluorodeoxyglucose PET and (b) characterizing functional interactions of neurotransmitter systems by assaying drug-induced displacement of specific receptor ligands. These study designs reflect a paradigm shift where functional coupling of brain regions and interaction of different neurotransmitter systems are seen as the basis for a multitransmitter hypothesis of schizophrenia. In this view, any disturbance in the self-regulatory process is reflected in the loss of functional interaction between systems. An overview of recent studies and their possible clinical importance will be presented.

Time-dependent effects of a haloperidol challenge on energy metabolism in the normal human brain

Positron emission tomography and the fluorodeoxyglucose method were used to measure regional brain metabolism before and 2 h after haloperidol (5 mg, i.m.) in 11 young normal men. These data were compared with measures obtained from nine previously studied normal men who had received no drug intervention. Although a previously published study had demonstrated significantly decreased metabolism in whole brain, neocortex, limbic cortex, thalamus, and caudate nucleus 12 h after a 5-mg dose of haloperidol, the present 2-h study did not show significant metabolic changes despite the fact that significant extrapyramidal effects occurred. Taken together, these studies demonstrate differences in the temporal organization of behavioral and metabolic responses to haloperidol challenge.

Effects of haloperidol challenge on regional cerebral glucose utilization in normal human subjects

OBJECTIVE

Positron emission tomography and the fluorodeoxyglucose (FDG) method were used to determine the brain's metabolic response to neuroleptic challenge in a normal, disease-free state.

METHOD

FDG measurements were obtained before and 12 hours after administration of 5 mg of haloperidol to 12 young normal men. These values were compared with test-retest FDG measures obtained from nine normal male control subjects who received no drug intervention.

RESULTS

After haloperidol administration, the haloperidol subjects showed significantly lower glucose utilization in the neocortex, limbic cortex, thalamus, and caudate nucleus but not in the putamen or cerebellum. After adjustment for global effects, significant reductions were still evident in the frontal, occipital, and anterior cingulate cortex, whereas the putamen and cerebellum showed significant increases.

CONCLUSIONS

This study, measuring the brain's metabolic response to acute receptor blockade, is a first step in the development of an assay of CNS pharmacological activity. By determining the response to neuroleptic challenge in a normal state, the study establishes a comparison group for determining response to challenge in various psychiatric conditions.

Diminished cerebral metabolic response to motor stimulation in schizophrenics: a PET study

Positron emission tomography (PET) and the deoxyglucose method were used to measure cerebral metabolism in 14 normals and 13 schizophrenics at rest and during performance of simple and complex finger-movement sequences. The normals, but not the schizophrenics, showed significant metabolic activation in mesial frontal and contralateral sensorimotor and premotor regions during the complex movement. The relative metabolism of schizophrenics was significantly lower than normal in frontal regions and higher than normal in thalamus and basal ganglia under all scanning conditions. The results suggest that schizophrenics may have a brain dysfunction which limits their capacity to produce a focal metabolic response to stimulation in several functionally distinct brain regions.

Importance of pharmacologic control in PET studies: effects of thiothixene and haloperidol on cerebral glucose utilization in chronic schizophrenia

This study compares the effects of two neuroleptic drugs with different pharmacologic characteristics (thiothixene and haloperidol) on cerebral glucose utilization in chronic schizophrenic inpatients. Positron emission tomographic (PET) scans were obtained from all subjects in a neuroleptic-free condition and again after 4-6 weeks of neuroleptic treatment. Eight subjects were treated with thiothixene and 12 with haloperidol. Thiothixene and haloperidol had different metabolic effects. For example, all thiothixene-treated subjects showed increased whole brain glucose utilization; all but one haloperidol-treated subject showed decreased utilization. Different patterns of relative prefrontal and striatal metabolism were also observed. These results highlight the importance of controlling for the effects of neuroleptic treatment and indicate the difficulty of interpreting data from studies with complex or poorly defined drug regimens.

Stability of resting deoxyglucose metabolic values in PET studies of schizophrenia

Positron emission tomography (PET) and the deoxyglucose method were used to determine the test-retest stability of regional cerebral glucose metabolism in 8 male schizophrenic patients and 11 normal control subjects, scanned twice under baseline (resting) conditions. Normal and schizophrenic subjects showed comparable stability of regional metabolism. When the regional values were scaled to compensate for the effects of changes in whole brain metabolism, the resulting mean regional changes were reduced to about 1-2% in both groups. This study demonstrates that the baseline resting state is an appropriate reference state for schizophrenic subjects in deoxyglucose PET experiments.

Reproducibility of cerebral glucose metabolic measurements in resting human subjects

Positron emission tomography with 11C-2-deoxyglucose was used to determine the test-retest variability of regional cerebral glucose metabolism in 22 young normal right-handed men scanned twice in a 24-h period under baseline (resting) conditions. To assess the effects of scan order and time of day on variability, 12 subjects were scanned in the morning and afternoon of the same day (a.m.-p.m.) and 10 in the reverse order (p.m.-a.m.) with a night in between. The effect of anxiety on metabolism was also assessed. Seventy-three percent of the total subject group showed changes in whole brain metabolism from the first to the second measurement of 10% or less, with comparable changes in various cortical and subcortical regions. When a scaling factor was used to equate the whole brain metabolism in the two scans for each individual, the resulting average regional changes for each group were no more than 1%. This suggests that the proportion of the whole brain metabolism utilized regionally is stable in a group of subjects over time. Both groups of subjects had lower morning than afternoon metabolism, but the differences were slight in the p.m.-a.m. group. One measure of anxiety (pulse at run 1) was correlated with run 1 metabolism and with the percentage of change from run 1 to run 2. No significant run 2 correlations were observed. This is the first study to measure test-retest variability in cerebral glucose metabolism in a large sample of young normal subjects. It demonstrates that the deoxyglucose method yields low intrasubject variability and high stability over a 24-h period.