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Michael Guarnieri

Publications and source records attributed to Michael Guarnieri.

16 recordsLinked to original sources
PubMed2006

Intracranial drug-delivery scaffolds: biocompatibility evaluation of sucrose acetate isobutyrate gels.

INTRODUCTION: Sucrose acetate isobutyrate (SAIB) is a water insoluble, biodegradable gel used for controlled-release oral and subcutaneous drug delivery. We investigated SAIB compatibility in the rat central nervous system (CNS) by implanting solutions of SAIB in adult and in neonatal brains. METHODS: 10-15 microL solutions of SAIB gels in 0-30% ethanol were injected into the cerebral cortex of adult Fischer 344 rats. Control animals were implanted with a 10 mg biodegradable poly anhydride copolymer of poly [bis (p-carboxyphenoxy) propane] anhydride and sebacic acid (PCPP:SA). Adult rats were evaluated for signs of pain and distress, including changes in posture, facial signs, and grooming behavior. 1-2 microL solutions of SAIB gels in 15% ethanol were injected into brains of 12-24 h-old rats. Neonatal rats were evaluated for survival. Adult and neonatal brains were examined by histopathology 3-48 days after implant. RESULTS: Gel implants produced elliptical compression of cortical tissue, cell loss, and inflammation. Cell loss appeared to be confined to the implantation wound and associated neuronal fields. In adult rats, neurophil compression, inflammation, and cell loss appeared similar with the 10-mg PCPP:SA implants and the 10-mg SAIB implants. There was no clinical evidence of pain or distress from SAIB implants. 1-2 microL implants of SAIB-15% ethanol had no effect on survival of neonatal animals. CONCLUSION: Brain implants of SAIB induce a mild to moderate inflammatory response and associated neuronal cell damage. The implants appeared to be biocompatible in adult and neonatal animals. These results suggest that further studies of SAIB as an injectable drug-delivery scaffold for CNS therapeutic agents are warranted.

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PubMed2006

Point mutations upstream of hepatitis B virus core gene affect DNA replication at the step of core protein expression.

The pregenomic RNA directs replication of the hepatitis B virus (HBV) genome by serving both as the messenger for core protein and polymerase and as the genome precursor following its packaging into the core particle. RNA packaging is mediated by a stem-loop structure present at its 5' end designated the epsilon signal, which includes the core gene initiator AUG. The precore RNA has a slightly extended 5' end to cover the entire precore region and, consequently, directs the translation of a precore/core protein, which is secreted as e antigen (HBeAg) following removal of precore-derived signal peptide and the carboxyl terminus. A naturally occurring G1862T mutation upstream of the core AUG affects the bulge of the epsilon signal and generates a "forbidden" residue at the -3 position of the signal peptide cleavage site. Transfection of this and other mutants into human hepatoma cells failed to prove their inhibition of HBeAg secretion but rather revealed great impairment of genome replication. This replication defect was associated with reduced expression of core protein and could be overcome by a G1899A covariation, or by nonsense or frameshift mutation in the precore region. All these mutations antagonized the G1862T mutation on core protein expression. Cotransfection of the G1862T mutant with a replication-deficient HBV genome that provides core protein in trans also restored genome replication. Consistent with our findings in cell culture, HBV genotype A found in African/Asian patients has T1862 and is associated with much lower viremia titers than the European subgroup of genotype A.

Amino Acid Sequence↗
PubMed2006

Local infusion therapy in the monkey brainstem: technical considerations.

This chapter assesses the safety of freehand placement of an infusion catheter (outer diameter, 0.3 mm) in brainstems of cynomolgus monkeys (Macaca fascicularis) for local infusion therapy. A posterior midline approach through the cerebellum and roof of the fourth ventricle was used to implant catheters into a pontine target area. Computer tomography (CT), magnetic resonance imaging (MRI), and histology were used to examine the position of the implants. The freehand placement of a catheter resulted in approximately 5-mm variations in anterior-posterior and dorsal-ventral locations of the targeted implantation site. No evidence of morbidity from the surgery, or from the infusion process was present. In conclusion, small-diameter catheters for chronic drug infusions can be implanted safely into the brainstem, an eloquent region that has been considered surgically inoperable. Infusion systems may offer a minimally invasive, generally applicable tool to provide chronic therapy for central nervous system (CNS) lesions.

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PubMed2005

A novel brainstem tumor model: guide screw technology with functional, radiological, and histopathological characterization.

OBJECT: Survival rates for high-grade brainstem tumors are approximately 10% and optimal therapy has yet to be determined. Development of a satisfactory brainstem tumor model is necessary for testing new therapeutic paradigms that may prolong survival. The authors report the technique, functional progression, radiological appearance, and histopathological features of a novel brainstem tumor model in rats. METHODS: Thirty female Fischer 344 rats were randomized (10 animals/group) to receive an injection of either 3 ml of 9L gliosarcoma cells (100,000 cells), 3 ml of F98 glioma cells (100,000 cells), or 3 ml of medium (Dulbecco modified Eagle medium) into the pontine tegmentum of the brainstem. Using a cannulated guide screw system implanted in the skull of the animal, rats in each group were injected at coordinates 1.4 mm to the right of the sagittal and 1 mm anterior to the lambdoid sutures, at a depth of 7 mm from the dura mater. The angle of the syringe during injection was anteflexed 5 degrees from the vertical. Postoperatively, the rats were evaluated for neurological deficits by using an automated rotarod test. High-resolution [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) fused with computerized tomography (CT) scans were acquired pre- and postoperatively through the onset of hemiparesis and correlated accordingly. Kaplan-Meier curves were generated for survival and disease progression, and brains were processed postmortem for histopathological investigation. The 9L and F98 tumor cells grew in 95% of the animals in which they were injected and resulted in a statistically significant mean onset of hemiparesis of 16.5 6 0.56 days (p = 0.001, log-rank test), compared with animals in the control group, which had no neurological deficits by Day 45. The FDG-PET studies coregistered with CT scans demonstrated space-occupying brainstem lesions, and this finding was confirmed by histological studies. Animals in the control group showed no functional, radiological, or pathological signs of tumor. CONCLUSIONS: Progression to hemiparesis was consistent in all tumor-injected animals, with predictable onset of symptoms occurring approximately 17 days postsurgery. The histopathological and radiological characteristics of the 9L and F98 brainstem tumors were comparable to those of aggressive primary human brainstem tumors. Establishment of this animal tumor model will facilitate the testing of new therapeutic paradigms for the treatment of these lesions.

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PubMed2005

Experimental models of brainstem tumors: development of a neonatal rat model.

OBJECTIVE: Brainstem tumor models are required to advance the treatment for diffuse pontine gliomas in children. The feasibility of creating an experimental rodent model by inoculating newborn pups with tumor cells was examined. The study was performed to create an animal model for diffuse brainstem tumors. METHODS: Eighty-two Fischer rat pups aged 12-24 h were anesthetized by hypothermia. The brainstem was injected with saline to identify anatomical coordinates for subsequent tumor cell challenges. The newborn pups were then inoculated with F98 (n=30) or 9L (n=30) glioma cells. Animals were returned to their mother for nursing. Tumor growth was assessed by survival and histopathology. RESULTS: Twenty-one percent of the saline-treated animals (17 out of 82) and 5% of the tumor cell-challenged pups (3 out of 60) were eliminated by their mothers. Inoculations with 9L and F98 cells produced brainstem tumors in 83% (24 out of 29) and 93% of animals (26 out of 28) respectively that were evaluated. CONCLUSIONS: Our results demonstrate that neonatal rat models for brainstem tumors can be prepared using known injection coordinates and orthotopic cell lines. Decreasing rates of maternal removal during the course of the work suggests that the method involves a learning curve.

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PubMed2005

Effect of mutating the two cysteines required for HBe antigenicity on hepatitis B virus DNA replication and virion secretion.

Hepatitis B virus (HBV) variants with impaired expression of e antigen (HBeAg) frequently arise at the chronic stage of infection, as exemplified by precore and core promoter mutants. Since an intramolecular disulfide bond maintains the secondary structure of HBeAg, we explored effect of missense mutations of either cysteine codon. Consistent with earlier reports, substitution of each cysteine rendered HBeAg nearly undetectable. With underlying nucleotide changes at the loop of pregenome encapsidation signal, the C-7 mutants were severely impaired in pregenomic RNA packaging and hence DNA replication. Although none of the missense mutations at C61 reduced DNA replication, replacement with arginine, but not alanine, aspartic acid, phenylalanine, or serine, blocked virion secretion. Consistent with the detection of C61R genome from a patient serum, secretion block of the C61R mutant could be overcome by co-expression of wild-type core protein. In conclusion, point mutations of the C61 codon may generate viable HBeAg-negative variants.

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PubMed2005

Infusion rates and drug distribution in brain tumor models in rats.

OBJECT: The aim of this study was to investigate the optimal delivery rates of chemotherapy for the treatment of central nervous system tumors and to determine whether local delivery can lower toxicity profiles and increase target concentrations of chemotherapy. METHODS: The authors used two brain tumor models in rats. Slow (1 microl/hour) and fast (10 microl/hour) pumps were used to deliver chemotherapy--carboplatin, doxorubicin, and a high-molecular-weight transferrin-doxorubicin conjugate to the brains of normal rats and rats previously injected with F98 or 9L rat brain tumor cells. Brains were cut in 1-mm sections rostral and caudal from the infusion point. Slices were analyzed for doxorubicin and platinum by fluorescence and atomic absorption, respectively. In the normal tissues, the volume of drug distribution is generally greater at the faster flow rate. In abnormal tissues, distribution is similar at slow and fast infusion rates for low-molecular-weight drugs and greater at slow rates for a high-molecular-weight targeted toxin. CONCLUSIONS: After local administration the distribution of chemotherapy appears to be significantly influenced by tumor metabolism. Additional studies are needed to determine the optimal delivery rates for the interaction of the drug with the targeted tumor.

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PubMed2004

Flexible versus rigid catheters for chronic administration of exogenous agents into central nervous system tissues.

INTRODUCTION: Neuropharmacology studies depend on consistency in drug delivery. Drug infusions into central nervous system (CNS) tissues have been described as unreliable. Speculation has focused on infusion pumps as the source of variation. This report demonstrates that the catheter may be a source of variability. The inconsistency can be significantly reduced by a change in catheter design. METHODS: Normal and tumor cell-challenged (abnormal) brains of Fischer rats were infused with small and large molecular weight cytotoxic drugs via rigid and flexible catheters placed directly into the parenchyma. Coronal tissue sections rostral and caudal to the infusion point were analyzed for drug concentrations. Carboplatin, estimated through atomic absorption assays, and doxorubicin and transferrin-bound doxorubicin, measured by fluorescent spectroscopy, were mapped in serial sections at various distances from the infusion point. RESULTS: The expected drug distribution pattern approximates a bell-shaped curve with a maximum drug concentration near the infusion point and approximately equal, declining concentrations rostral and caudal to the infusion. This expected distribution was found in only 10 of the 17 normal brains and 15 of the 28 abnormal brains infused with a rigid catheter. In contrast, 10 of the 10 normal brains and 16 of the 16 abnormal rat brains infused with a flexible catheter had the expected distribution pattern. The distribution pattern was not associated with the molecular weight of the infused drug. CONCLUSION: Replacement of rigid infusion tubes with flexible tubing increases the reliability of local CNS drug infusions. Rigid catheters may allow backflow of the infused drug along the path of the catheters into the subdural space.

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PubMed2004

Living with achondroplasia: quality of life evaluation following cervico-medullary decompression.

Achondroplasia is the most common of the heritable skeletal dysplasias. Cervico-medullary compression is a frequently encountered and potentially lethal neurological complication. Cervico-medullary decompression (CMD) at the foramen magnum is often employed to relieve the pressure on the emerging cervical cord. Given the inherent risks associated with major surgery, there has been a substantial debate regarding the best criteria for CMD. Our objectives for this study are to explore the quality of life of patients who had undergone CMD, and to assess whether surgery is associated with mortality and increased long-term morbidity. A Medical Outcome Study 36-item Short Form General Health Survey designed to evaluate eight general health concepts as well as achondroplasia-related issues, was administered to patients assessed in the neurosurgery department in Johns Hopkins Hospital between 1977 and 1998. One hundred and sixty-seven patients were eligible for inclusion. Forty-three could not be contacted, and two refused consent. One hundred and twenty-two patients were assessed. Fifty-six (46%) individuals had CMD and 66 (54%) did not. There was 1 case of mortality in the CMD group and 12 cases in the non-CMD group. In the non-CMD group, all deaths, as far as we know, were unrelated to cervico-medullary compression. In this cohort of surviving patients (n = 109), the quality of life of the 55 (50.5%) who had undergone CMD is comparable to that of the 54 (49.5%) who did not have surgery, controlled for age and sex. CMD is indicated for patients with achondroplasia with significant symptomatic foramen magnum compression. It can be life saving. It can abolish profound central apnea that may cause sudden death and alleviate neurological complications associated with damage of the significantly compressed spinal cord. With regards to long-term outcome evaluation, the quality of life of individuals with achondroplasia who had CMD is similar to those age- and sex-matched patients who did not have this surgery. Moreover, CMD, with all its inherent surgical risks, does not appear to be associated with higher mortality or increased long-term morbidity.

Achondroplasia↗
PubMed2004

Long-term effects of carboplatin brainstem infusions on hearing thresholds in monkeys.

OBJECTIVE: To isolate the central auditory neurotoxicity of carboplatin from its well-established ototoxic effects. DESIGN: The "best-case scenario" of targeted drug delivery to brain cancer was simulated by infusing carboplatin directly into the brainstem of cynomolgus monkeys with chronically implanted catheters. Because this manner of drug administration produced low levels of carboplatin in spinal fluid and blood, it was assumed that resulting deficits were dictated by the central auditory neurotoxicity of platinum compounds and not peripheral ototoxic effects. The magnitude of this hearing loss was estimated by comparing the auditory brainstem response thresholds of treated monkeys with results from normal controls. SUBJECTS: Six adult male cynomolgus monkeys (Macaca fascicularis) weighing 4 to 6 kg (3 received carboplatin treatment and 3 served as normal controls). INTERVENTION: Brainstem infusions of carboplatin. RESULTS: The average threshold of carboplatin-treated monkeys was elevated 8.8 dB (SD = 7.3 dB) relative to normal controls 6 months after the termination of drug delivery and increased to 10.7 dB with less variation between subjects (SD = 5.6 dB) 1 year after drug treatment. Although small in magnitude, the hearing loss was statistically significant (P<.05). CONCLUSIONS: Brainstem infusions of carboplatin induced some degree of hearing impairment in all treated monkeys. These threshold elevations were modest compared with the ototoxic effects that have been reported after systemic doses of carboplatin. Our findings suggest that the neurotoxic sensitivity of cochlear hair cells is not shared by neurons in the central auditory pathways. As a result, methods for reducing the ototoxic effects of chemotherapy remain a viable strategy for preserving auditory function in patients with brain cancer.

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PubMed2004

Modulation of hepatitis B virus secretion by naturally occurring mutations in the S gene.

Alteration in hepatitis B virus (HBV) secretion efficiency may have pathological consequences. Naturally occurring mutations that regulate virion secretion have not been defined. We recently identified HBV genomes displaying high (4B), substantially reduced (3.4), or negative (4C) virion secretion. In the present study, the underlying mutations were mapped. A T552C point mutation in the 4B genome was responsible for its enhanced virion secretion, whereas a G510A mutation in 3.4 and G660C in 4C impaired virus secretion. The three point mutations generate M133T, G119E, and R169P substitutions in the S domains of viral envelope proteins, respectively, without modifying the coding capacity of the overlapping polymerase gene. The mutated residues are predicted to lie in the luminal side of the endoplasmic reticulum (ER) or to be embedded in the ER membrane and thus are not involved in contact with core particles during envelopment. Of the two mutations inhibitory of virion secretion, G510A greatly reduced small envelope protein (hepatitis B surface antigen [HBsAg]) levels both inside cells and in culture medium, whereas G660C specifically abolished HBsAg secretion. Surprisingly, a T484G mutation in the 4B genome, generating an I110M substitution in the S domain, could also reduce HBsAg secretion and block virion secretion. However, its inhibitory effect was suppressed in the 4B genome by the T552C mutation, the enhancer of virion secretion. T552C can also override the inhibitory G510A mutation, but not the G660C mutation. These findings suggest a hierarchy in the regulation of virion secretion and a close link between defective virion secretion and impaired HBsAg formation or secretion.

Amino Acid Sequence↗
PubMed2003

A surgical technique for safely placing a drug delivery catheter into the pons of primates: preliminary results of carboplatin infusion.

OBJECTIVE: We sought to develop a neurosurgical procedure to access the pons with a drug delivery device for chronic therapy and collect preliminary data on the toxicity of direct infusions of carboplatin in primates. METHODS: We made midline incisions on five cynomolgus monkeys, identified the inion, made a burr hole 2.5 cm below the inion, and inserted a catheter through the cerebellum into the roof of the pons. Pumps that infused saline for 90 days or carboplatin solutions for 30 to 35 days at 10 microl/d were placed subcutaneously in the low cervical/high thoracic region. Monkeys were assessed by computed tomography and magnetic resonance imaging, laboratory studies, daily neurological observation, postmortem examinations, and histopathology. RESULTS: Monkeys infused with saline and 82 microg of carboplatin remained neurologically intact throughout the infusion periods. Serial imaging showed that the catheter tip was in the pons and revealed no evidence of hemorrhage, edema, or migration. Two monkeys infused with up to 850 microg of carboplatin showed hyperintense magnetic resonance imaging signals at Days 15 and 18 and neurological deficits at approximately Week 3. Platinum levels greater than 10 ng/mg tissue were detected over a distance of 1 cm in tissue slices. Histopathology demonstrated significant tissue necrosis around the tip of the catheter. CONCLUSION: The pons of monkeys is safely accessed with a catheter for drug delivery by using a posterior midline approach. Clinical observations, radiographic imaging, and laboratory tests of animals infused with saline for 3 months or 0.26 mg/ml of carboplatin for 1 month were unremarkable. Neurotoxicity was seen with dose levels of 2.6 mg/ml of drug for 1 month. This procedure offers opportunities for examining the toxicity of brainstem antitumor therapy in primates.

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PubMed2002

Toxicity of intracranial and intraperitoneal O6-benzyl guanine in combination with BCNU delivered locally in a mouse model.

PURPOSE: The DNA-repair protein, O6-alkylguanine-DNA alkyl transferase, may account for resistance of CNS tumors to DNA-alkylating drugs, such as bis-(2-chloroethyl)-1-nitrosourea (BCNU). The therapeutic effects of BCNU can be potentiated by inhibiting the repair protein with an alkylated guanine analog, O6-benzyl guanine (O6BG). To investigate potential toxicity of this inhibition, we examined the effects of O6BG in mice treated with intracranial (i.c.) BCNU given via a biodegradable polymer. METHODS: Mice were treated with escalating doses of BCNU chronically delivered i.c., and with chronically delivered O6BG. The O6BG was delivered via a 7-day intraperitoneal (i.p.) or i.c. osmotic minipump. Toxicity of the combination therapies was measured from survival data. Bone marrow response was estimated from white blood cell counts. RESULTS: Combining systemic (i.p.) O6BG with locally (i.c.) delivered BCNU resulted in a decrease in the maximum tolerated dose (MTD) of local BCNU. With local delivery of O6BG, the MTD of BCNU in combination with O6BG was increased. CONCLUSIONS: Based on the results of this study, a dose escalation study will be necessary when combining systemic O6BG with the higher doses of i.c. BCNU.

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PubMed2002

New approach to tumor therapy for inoperable areas of the brain: chronic intraparenchymal drug delivery.

Because the brainstem has little functional redundancy, diffuse lesions have been regarded as inoperable. To determine whether local drug therapy can prolong survival in a rodent model of a tumor in such eloquent tissue, lethal doses of F98 and 9L tumor cells were injected into the brainstems of Fischer 344 rats. Five days after inoculations, 0.5 mg/ml solutions of carboplatin were infused at 1 microl/h for 7 days. Compared to control groups that survived 13-17 days with F98 tumors and 22-23 days with 9L tumors, animals locally infused with 0.1 mg of carboplatin survived 27-30 days (Prob > Chi Sq = 0.0003), and 32 days (Prob > Chi Sq = 0.01), respectively. Measurements of tissue platinum levels at autopsy suggested that infusions distributed pharmacologically relevant levels of carboplatin through a volume of tissue at least 0.5 cm in diameter. The results suggest that chronic low-flow infusions provide a promising approach to therapy for CNS lesions in tissues considered to be inoperable.

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