Microdialysis evaluation of clozapine and N-desmethylclozapine pharmacokinetics in rat brain

A significant barrier to realization of the full potential of clozapine as a therapeutic agent in the treatment of schizophrenia is the substantial interpatient variability that exists along the therapeutic continuum of no response-efficacious response-adverse response. Genetic polymorphisms that manifest as highly variable pharmacodynamic and pharmacokinetic measures are its expected causes. To support investigations that seek to understand these causes, the plasma and central nervous system pharmacokinetics of clozapine were determined in rats, the latter using microdialysis sampling. Results obtained with clozapine and N-desmethylclozapine, a pharmacologically active human metabolite that was administered to a separate group of animals, support a conclusion of net carrier-mediated efflux of both compounds across the blood-brain barrier. These results are supported by the replication of published findings regarding the passive transport and net efflux transport of two model compounds, escitalopram and risperidone, respectively. The results obtained with clozapine and N-desmethylclozapine are considered a first step in the development of preclinical pharmacokinetic-pharmacodynamic models that will support deeper mechanistic studies of clozapine in in vivo pharmacology, as well as the development of translational models that augment pharmacogenetic investigations that seek to improve the safety and efficacy of clozapine therapeutic intervention in the treatment of schizophrenia.     

The role of somatostatin and dopamine D2 receptors in endocrine tumors

Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D(2) receptor (D(2)) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D(2) as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D(2) pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.     

IGF-I Bioactivity in an Elderly Population: Relation to Insulin Sensitivity, Insulin Levels, and the Metabolic Syndrome

OBJECTIVE

There is a complex relationship between IGF-I, IGF binding proteins, growth hormone, and insulin. The IGF-I kinase receptor activation assay (KIRA) is a novel method for measuring IGF-I bioactivity in human serum. We speculated that determination of IGF-I bioactivity might broaden our understanding of the IGF-I system in subjects with the metabolic syndrome. The purpose of our study was to investigate whether IGF-I bioactivity was related to insulin sensitivity and the metabolic syndrome.

RESEARCH DESIGN AND METHODS

We conducted a cross-sectional study embedded in a random sample (1,036 elderly subjects) of a prospective population-based cohort study. IGF-I bioactivity was determined by the IGF-I KIRA. Categories of glucose (in)tolerance were defined by the 2003 American Diabetes Association criteria. Insulin sensitivity was assessed by homeostasis model assessment. The Adult Treatment Panel III definition of the metabolic syndrome was used.

RESULTS

In subjects with normal fasting glucose and impaired fasting glucose, IGF-I bioactivity progressively increased with increasing insulin resistance, peaked at fasting glucose levels just below 7.0 mmol/l, and dropped at higher glucose levels. Mean IGF-I bioactivity peaked when three criteria of the metabolic syndrome were present and then declined significantly when five criteria of the metabolic syndrome were present.

CONCLUSIONS

We observed that IGF-I bioactivity was related to insulin sensitivity, insulin levels, and the metabolic syndrome. Our study suggests that there exists an inverse U-shaped relationship between IGF-I bioactivity and number of components of the metabolic syndrome. This observation contrasts with previous results reporting an inverse relationship between total IGF-I and components of the metabolic syndrome.A complex relationship exists between IGF-I, IGF binding proteins (IGFBPs), growth hormone (GH), and insulin. GH exerts potent effects on intermediary metabolism by antagonizing insulin action (1). IGF-I directly inhibits insulin secretion and increases insulin sensitivity (2). Insulin appears to be necessary for normal liver GH responsiveness, probably by maintaining liver GH receptor levels (3). However, chronic hyperinsulinemia reduces GH receptor expression and signaling in the liver (4,5). The majority of circulating IGF-I is bound to six IGFBPs that are important in determining IGF-I availability and activity (6).Recently, the IGF-I–specific kinase receptor activation assay (KIRA) was developed to determine circulating IGF bioactivity (7,8). This bioassay determines IGF-I bioactivity by measuring intracellular receptor auto-phosphorylation upon IGF-I binding. Unlike IGF-I immunoassays, the IGF-I KIRA takes into account the modifying effects of IGFBPs on the interaction between IGF-I and the IGF-I receptor (IGF-IR) (9). The aim of the present study was to investigate whether IGF-I bioactivity was related to insulin sensitivity, insulin levels, and the metabolic syndrome in an elderly population-based cohort.     

Intravenous glucose administration in fasting rats has differential effects on acylated and unacylated ghrelin in the portal and systemic circulation: a comparison between portal and peripheral concentrations in anesthetized rats

Ghrelin is produced by the gastrointestinal tract, and its systemic concentrations are mainly regulated by nutritional factors. Our aim was to investigate: 1) endogenous portal and systemic acylated and unacylated ghrelin levels (AG and UAG, respectively); 2) whether an iv glucose tolerance test (IVGTT) modifies AG and UAG; and 3) whether the liver passage plays a role in regulating systemic AG and UAG. To elucidate this, we evaluated the effects of IVGTT or saline injection on endogenous portal and systemic concentrations of glucose, insulin, AG, and UAG in anesthetized fasting rats. Hepatic extraction of insulin, AG, and UAG and the ratio of AG to UAG were also measured. IVGTT suppressed both portal (P < 0.03) and peripheral (P < 0.05) UAG, whereas it only blunted prehepatic, but not peripheral, AG. During fasting, hepatic clearance of UAG was 11%, and it was decreased to 8% by IVGTT. AG was cleared by the liver by 38% but unaffected by glucose. The AG to UAG ratio was higher in the portal than the systemic circulation, both in the saline (P < 0.004) and IVGTT (P < 0.0005) rats. In conclusion, this study shows that: 1) the ratio of AG to UAG is very low in the portal vein and decreases further in the systemic circulation; 2) IVGTT in anesthetized fasting rats inhibits UAG, whereas it only blunts prehepatic, but not systemic, AG; and 3) hepatic clearance of AG is much higher than that of UAG. Thus, our results suggest that peripheral AG metabolic regulation and action are mainly confined within the gastrointestinal tract.     

The obesity paradox: association of obesity with improved survival in medically managed severe aortic stenosis

INTRODUCTIONThe obesity paradox, where obesity is associated with improved survival, has been described in patients undergoing haemodialysis and in those with heart failure. It was also demonstrated in patients undergoing valve replacement for aortic stenosis (AS). We explored this phenomenon in medically managed severe AS.METHODS154 patients with medically managed severe AS (aortic valve area index [AVAi] < 0.6 cm²/m²; mean pressure gradient > 40 mmHg and peak velocity > 400 cm/s) and preserved left ventricular ejection fraction (> 50%) were categorised into the obese (body mass index [BMI] Asian cut-off ≥ 27.5 kg/m²) and non-obese groups. Their clinical and echocardiographic profiles were compared.RESULTS24 (15.6%) patients were obese. Obese patients were similar to non-obese patients in age (68.5 ± 11.6 years vs. 68.9 ± 13.1 years) but had higher prevalence of cardiovascular risk factors. Left atrial diameter (43.7 ± 6.7 mm vs. 38.5 ± 10.2 mm) was larger in obese patients, while left ventricular outflow tract diameter (19.5 ± 1.7 mm vs. 20.4 ± 2.1 mm) was smaller. Despite lower AVAi in obese patients (0.36 ± 0.10 cm²/m² vs. 0.43 ± 0.11 cm²/m²), there was lower mortality (37.5% vs. 41.0%, log-rank 4.06, p = 0.045) on follow-up (8.0 ± 5.7 years). After adjusting for age and AVAi, higher BMI ≥ 27.5 kg/m² remained protective for mortality (hazard ratio 0.38, 95% confidence interval 0.15 to 0.98, p = 0.046).CONCLUSIONWe demonstrated that obesity was associated with improved survival in severe AS despite lower AVAi and increased prevalence of cardiovascular risk factors.     

Comprehensive multiplexed immune profiling of the ductal carcinoma in situ immune microenvironment regarding subsequent ipsilateral invasive breast cancer risk

Background Ductal carcinoma in situ (DCIS) is treated to prevent subsequent ipsilateral invasive breast cancer (iIBC). However, many DCIS lesions will never become invasive. To prevent overtreatment, we need to distinguish harmless from potentially hazardous DCIS. We investigated whether the immune microenvironment (IME) in DCIS correlates with transition to iIBC.Methods Patients were derived from a Dutch population-based cohort of 10,090 women with pure DCIS with a median follow-up time of 12 years. Density, composition and proximity to the closest DCIS cell of CD20⁺ B-cells, CD3⁺CD8⁺ T-cells, CD3⁺CD8⁻ T-cells, CD3⁺FOXP3⁺ regulatory T-cells, CD68⁺ cells, and CD8⁺Ki67⁺ T-cells was assessed with multiplex immunofluorescence (mIF) with digital whole-slide analysis and compared between primary DCIS lesions of 77 women with subsequent iIBC (cases) and 64 without (controls).Results Higher stromal density of analysed immune cell subsets was significantly associated with higher grade, ER negativity, HER-2 positivity, Ki67 ≥ 14%, periductal fibrosis and comedonecrosis (P < 0.05). Density, composition and proximity to the closest DCIS cell of all analysed immune cell subsets did not differ between cases and controls.Conclusion IME features analysed by mIF in 141 patients from a well-annotated cohort of pure DCIS with long-term follow-up are no predictors of subsequent iIBC, but do correlate with other factors (grade, ER, HER2 status, Ki-67) known to be associated with invasive recurrences.Subject terms: Prognostic markers, Imaging the immune system, Breast cancer, Cancer microenvironment, Translational research

     

Retrospective first-in-human use of the LithoVue™ Elite ureteroscope to measure intrarenal pressure

Objective

To report on our first-in-human experience using the LithoVue Elite™ ureteroscope (Boston Scientific Corp., Marlborough, MA, USA) to measure intrarenal pressure (IRP) during flexible ureteroscopy.

Patients and Methods

A single-arm retrospective observational analysis was performed in 50 consecutive patients undergoing ureteroscopic lithotripsy using the LithoVue Elite™ system with pressure sensing capability between April 2022 and February 2023 at two centres. A pressure bag set at 150 mmHg or hand irrigation with a 60-mL syringe was used for irrigation and a ureteric access sheath (UAS) was placed at the physician's discretion. Median and maximum IRPs, and relative cumulative time exceeding 20, 40, 60, 80, 100, 120, 140, 160, and 200 mmHg per total procedure time were analysed. The two-sample Mann–Whitney U-test was used, with statistical significance set at P < 0.05.

Results

The median (interquartile range [IQR]) patient age and body mass index (BMI) was 62.5 (46.7–68.2) years and 27.6 (23.3–32.1) kg/m², respectively. During the median (IQR) total procedure time of 31.9 (17.4–44.9) min, the median and maximum IRPs were 28.5 (20.0–47.5) and 174.0 (133.5–266.0) mmHg, respectively. IRP remained at <60 mmHg during 92% of the procedure times. Patients with Asian ethnicity, and those without pre-stenting or UAS use exhibited longer cumulative/total durations exceeding pre-defined IRP cut-off values. The smaller 10/12-F UAS did not lower pressures as much as the 11/13-F or 12/14-F UAS (P < 0.001). Age, diabetes, hypertension, preoperative α-blockade, stone size, and BMI did not show any statistically significant associations with IRP.

Conclusions

The IRP can now be routinely measured during ureteroscopy. Patients had a median IRP of 28.5 mmHg and a maximum of 174 mmHg. Using a smaller UAS (10/12 F), Asian ethnicity, and tight ureters were found to have higher IRPs.