A randomized controlled laboratory study on the long-term effects of methylphenidate on cardiovascular function and structure in rhesus monkeys

Chicken Juice Enhances C. jejuni NCTC 11168 Biofilm Formation with Distinct Morphological Features and Altered Protein Expression

Campylobacter jejuni is the foodborne pathogen causing most gastrointestinal infections. Understanding its ability to form biofilms is crucial for devising effective control strategies in food processing environments. In this study, we investigated the growth dynamics and biofilm formation of C. jejuni NCTC 11168 in various culture media, including chicken juice (CJ), brain heart infusion (BHI), and Mueller Hinton (MH) broth. Our results demonstrated that C. jejuni exhibited a higher growth rate and enhanced biofilm formation in CJ and in 1:1 mixtures of CJ with BHI or MH broth compared to these measures in BHI or MH broth alone. Electron microscopy unveiled distinct morphological attributes of late-stage biofilm cells in CJ, including the presence of elongated spiral-shaped cells, thinner stretched structures compared to regular cells, and extended thread-like structures within the biofilms. Proteomic analysis identified significant alterations in protein expression profiles in C. jejuni biofilms, with a predominance of downregulated proteins associated with vital functions like metabolism, energy production, and amino acid and protein biosynthesis. Additionally, a significant proportion of proteins linked to biofilm formation, virulence, and iron uptake were suppressed. This shift toward a predominantly coccoid morphology echoed the reduced energy demands of these biofilm communities. Our study unlocks valuable insights into C. jejuni's biofilm in CJ, demonstrating its adaptation and survival.

Use of methylphenidate and reporting of valvular heart disease: Global pharmacovigilance analysis in children and adults

INTRODUCTION

Methylphenidate (MPH) is a common treatment of attention-deficit/hyperactivity disorder (ADHD). Concern has been raised regarding its cardiovascular safety, partly in relation with its micromolar affinity for the 5-HT2B receptor, whose activation may result in valvular heart disease (VHD).

METHODS

To explore the association between the use of MPH and VHD reporting, we performed a disproportionality analysis within the WHO global safety database (VigiBase) using data, since inception until March 6th 2024, from: (i) the full database and (ii) different age groups (children/adolescents 6-17 years; adults 18-64 years). To avoid competition bias, safety reports with amphetamine-like appetite suppressants were excluded. Disproportionality was expressed using reporting odds-ratio (ROR) and its 95% confidence interval (CI).

RESULTS

Of 29 129 spontaneous reports with MPH, 23 VHD cases (7.9 per 10 000 reports) were identified, including 13 adults and 10 children. Most cases concerned injury on the mitral valve. A disproportionate reporting was observed overall (ROR 1.6, 95% CI 1.1-2.4). Analysis according to age group found that disproportionality in VHD reporting was found in adults only (ROR 2.7, 95% CI 1.6-4.7) but not in children/adolescents (ROR 1.7, 95% CI 0.9-3.2). Furthermore, amongst MPH users only, VHD reporting was higher in adults compared to children (ROR 2.7, 95% CI 1.2-6.3).

CONCLUSION

VHD reporting appears rare with MPH compared to other adverse events and is increased in adults only. Our findings support a potential safety signal of VHD in adults exposed to MPH. A risk in that population cannot be excluded and requires further assessment.

Discontinuation of methylphenidate after long-term exposure in nonhuman primates

Attention-deficit hyperactivity disorder (ADHD) is a common human neurobehavioral disorder that usually begins in early childhood. Methylphenidate (MPH) has been used extensively as a first-line medicine for the treatment of ADHD. Since ADHD is often diagnosed in early childhood and can persist for the entire lifespan, individuals may take MPH for many years. Given that in the course of one's lifetime a person may stop taking MPH for periods of time, or may implement lifestyle changes that may reduce the need for MPH entirely, it is important to understand how cessation of MPH affects the adult brain following long-term use of MPH. The blockage of the dopamine transporter (DAT) and the norepinephrine transporter (NET) by MPH may help with ADHD symptoms by boosting monoamine levels in the synapse. In the present study, microPET/CT was used to investigate possible neurochemical alterations in the cerebral dopamine system after cessation of long-term MPH administration in nonhuman primates. MicroPET/CT images were collected from adult male rhesus monkeys 6 months after they stopped receiving vehicle or MPH following 12 years of chronic treatment. The neurochemical status of brain dopaminergic systems was evaluated using the vesicular monoamine transporter 2 (VMAT2) ligand [¹⁸F]-AV-133 and a tracer for imaging dopamine subtype 2 (D₂) and serotonin subfamily 2 (5HT₂) receptors, [¹⁸F]-FESP. Each tracer was injected intravenously and ten minutes later microPET/CT images were obtained over 120 min. The binding potential (BP) of each tracer in the striatum was obtained using the Logan reference tissue model with the cerebellar cortex time activity curve (TAC) as an input function. Brain metabolism was also evaluated using microPET/CT images of [¹⁸F]-FDG. [¹⁸F]-FDG was injected intravenously, and ten minutes later, microPET/CT images were obtained over 120 min. Radiolabeled tracer accumulation in regions of interest (ROIs) in the prefrontal cortex, temporal cortex, striatum, and cerebellum were converted into standard uptake values (SUVs). Compared to the vehicle control group, the BPs of [¹⁸F] AV-133 and [¹⁸F]-FESP in the striatum were not significantly altered in MPH treated groups. Additionally, no significant differences were detected in the SUVs of [¹⁸F]-FDG in the MPH treated group compared with control. This study demonstrates that 6 months after cessation of long-term, chronic MPH treatment, there are no significant neurochemical or neural metabolic changes in the central nervous system (CNS) of non-human primates (NHPs) and suggests that microPET imaging is helpful in assessing the status of biomarkers of neurochemical processes linked to chronic CNS drug exposure. (Supported by NCTR).

The effects of long-term methylphenidate administration and withdrawal on progressive ratio responding and T2 MRI in the male rhesus monkey

Methylphenidate is a frequently prescribed drug treatment for Attention-Deficit/Hyperactivity Disorder. However, methylphenidate has a mode of action similar to amphetamine and cocaine, both powerful drugs of abuse. There is lingering concern over the long-term safety of methylphenidate, especially in a pediatric population, where the drug may be used for years. We performed a long-term evaluation of the effects of chronic methylphenidate use on a behavioral measure of motivation in male rhesus monkeys. Animals were orally administered a sweetened methylphenidate solution (2.5 or 12.5 mg/kg, twice a day, Mon-Fri) or vehicle during adolescence and into adulthood. These animals were assessed on a test of motivation (progressive ratio responding), during methylphenidate treatment, and after cessation of use. Moreover, animals were evaluated with quantitative T₂ MRI about one year after cessation of use. During the administration phase of the study animals treated with a clinically relevant dose of methylphenidate generally had a higher rate of responding than the control group, while the high dose group generally had a lower rate of responding. These differences were not statistically significant. In the month after cessation of methylphenidate, responding in both experimental groups dropped compared to their previous level of performance (p = 0.19 2.5 mg/kg, p = 0.06 12.5 mg/kg), and responding in the control animals was unchanged (p = 0.81). While cessation of methylphenidate was associated with an acute reduction in responding, group differences were not observed in the following months. These data suggest that methylphenidate did not have a significant impact on responding, but withdrawal from methylphenidate did cause a temporary change in motivation. No changes in T₂ MRI values were detected when measured about one year after cessation of treatment. These data suggest that long-term methylphenidate use does not have a negative effect on a measure of motivation or brain function / microstructure as measured by quantitative T₂ MRI. However, cessation of use might be associated with temporary cognitive changes, specifically alteration in motivation. Importantly, this study modeled use in healthy individuals, and results may differ if the same work was repeated in a model of ADHD.

Genotoxicity evaluation using primary hepatocytes isolated from rhesus macaque (Macaca mulatta)

Non-human primates (NHPs) have played a vital role in fundamental, pre-clinical, and translational studies because of their high physiological and genetic similarity to humans. Here, we report a method to isolate primary hepatocytes from the livers of rhesus macaques (Macaca mulatta) after in situ whole liver perfusion. Isolated primary macaque hepatocytes (PMHs) were treated with various compounds known to have different pathways of genotoxicity/carcinogenicity and the resulting DNA damage was evaluated using the high-throughput CometChip assay. The comet data were quantified using benchmark dose (BMD) modeling and the BMD₅₀ values for treatments of PMHs were compared with those generated from primary human hepatocytes (PHHs) in our previous study (Seo et al. Arch Toxicol 2020, 2207-2224). The results showed that despite varying CYP450 enzyme activities, PMHs had the same sensitivity and specificity as PHHs in detecting four indirect-acting (i.e., requiring metabolic activation) and seven direct-acting genotoxicants/carcinogens, as well as five non-carcinogens that are negative or equivocal for genotoxicity in vivo. The BMD₅₀ estimates and their confidence intervals revealed species differences for DNA damage potency, especially for direct-acting compounds. The present study provides a practical method for maximizing the use of animal tissues by isolating primary hepatocytes from NHPs. Our data support the use of PMHs as a reliable surrogate of PHHs for evaluating the genotoxic hazards of chemical substances for humans.

MicroPET/CT assessment of neurochemical effects in the brain after long-term methylphenidate treatment in nonhuman primates

Methylphenidate (MPH) is a psychostimulant approved by the FDA to treatment Attention-Deficit Hyperactivity Disorder (ADHD). MPH is believed to exert its pharmacological effects via preferential blockade of the dopamine transporter (DAT) and the norepinephrine transporter (NET), resulting in increased monoamine levels in the synapse. We used a quantitative non-invasive PET imaging technique to study the effects of long-term methylphenidate use on the central nervous system (CNS). We conducted microPET/CT scans on young adult male rhesus monkeys to monitor changes in the dopaminergic system. We used [¹⁸F] AV-133, a ligand for the vesicular monoamine transporter 2 (VMAT2), and [¹⁸F]FESP a ligand for the D₂ and 5HT₂ receptors. In this study we evaluated the effects if chronic MPH treatment in the nonhuman primates (NHP). Two-year-old, male rhesus monkeys were orally administered MPH diluted in the electrolyte replenisher, Prang, twice a day, five days per week (M-F) over an 8-year period. The dose of MPH was gradually escalated from 0.15 mg/kg initially to 2.5 mg/kg/dose for the low dose group, and 1.5 mg/kg to 12.5 mg/kg/dose for the high dose group (Rodriguez et al., 2010). Scans were performed on Mondays, about 60 h after their last treatment, to avoid the acute effects of MPH. Tracers were injected intravenously ten minutes before microPET/CT scanning. Sessions lasted about 120 min. The Logan reference tissue model was used to determine the Binding Potential (BP) of each tracer in the striatum with the cerebellar cortex time activity curve as an input function. Both MP treatment groups had a lower [¹⁸F] AV-133 BP, although this failed to reach statistical significance. MPH treatment did not have a significant effect on The BP of [¹⁸F] FESP in the striatum. Long-term administration of MPH did not significant change any of the marker of monoamine function used here. These data suggest that, despite lingering concerns, long-term use of methylphenidate does not negatively impact monoamine function. This study also demonstrates that microPET imaging can distinguish differences in binding potentials of a variety of radiotracers in the CNS of NHPs. This approach may provide minimally-invasive biomarkers of neurochemical processes associated with chronic exposure to CNS medications. (Supported by NCTR).