Chemical and stereochemical aspects of propranolol metabolism. Diastereomeric 1-(1-hydroxy-2-propylamino)-3-(1-naphthoxy)-2-propanols produced by rat liver microsomal omega-hydroxylation

A new metabolic pathway of terminal hydroxylation (omega-hydroxylation) of the N-isopropyl group of propranolol (1) was established. Selected ion-monitoring GC-MS analysis, based on use of the synthesized mixture of diastereoisomers of 1-(1-hydroxy-2-propylamino)-3-(1-naphthoxy)-2-propanol (2) as a standard, established formation of both diastereoisomers of 2 as metabolites of 1. These diastereoisomers were formed in unequal amounts when 1, its hexadeuterated analogue 8 or heptadeuterated analogue 9, were incubated in the presence of the rat liver microsomal fraction. Authentic (2R,2"S)-2, obtained from the amide formed from (2S)-3-(1-naphthoxy)-2-hydroxypropionic acid [(2S)-5] and (2S)-alaninol by diborane reduction, facilitated examination of stereochemical aspects of this process. From incubations of the enantiomers of 1 and pseudoracemic propranolol [equimolar (2R)-propranolol-3,3-d2 and (2S)-propranolol-d0] in the presence of the rat liver microsomal fraction, we established that the diastereomeric products were formed in the order (2S,2"S)-2 approximately equal to (2S,2"R)-2 greater than (2R,2"R)-2 greater than (2R,2"S)-2. (2S)-1, which was metabolized to 2 to a greater extent than (2R)-1, showed no stereoselectivity, affording about equal amounts of (2S,2"S)-2 and (2S,2"R)-2. (2R)-1, which was metabolized to 2 to a lesser extent, afforded considerably more (2R,2"R)-2 than (2R,2"S)-2. omega-Hydroxylation was a minor metabolic pathway in the microsomal incubation. About 2000X less 2 than 1-amino-3-(1-naphthoxy)-2-propanol (3), the product of N-dealkylation of 1, was formed.     

Response of the ENPP1-Deficient Skeletal Phenotype to Oral Phosphate Supplementation and/or Enzyme Replacement Therapy: Comparative Studies in Humans and Mice

Inactivating mutations in human ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) may result in early-onset osteoporosis (EOOP) in haploinsufficiency and autosomal recessive hypophosphatemic rickets (ARHR2) in homozygous deficiency. ARHR2 patients are frequently treated with phosphate supplementation to ameliorate the rachitic phenotype, but elevating plasma phosphorus concentrations in ARHR2 patients may increase the risk of ectopic calcification without increasing bone mass. To assess the risks and efficacy of conventional ARHR2 therapy, we performed comprehensive evaluations of ARHR2 patients at two academic medical centers and compared their skeletal and renal phenotypes with ENPP1-deficient Enpp1^asj/asj mice on an acceleration diet containing high phosphate treated with recombinant murine Enpp1-Fc. ARHR2 patients treated with conventional therapy demonstrated improvements in rickets, but all adults and one adolescent analyzed continued to exhibit low bone mineral density (BMD). In addition, conventional therapy was associated with the development of medullary nephrocalcinosis in half of the treated patients. Similar to Enpp1^asj/asj mice on normal chow and to patients with mono- and biallelic ENPP1 mutations, 5-week-old Enpp1^asj/asj mice on the high-phosphate diet exhibited lower trabecular bone mass, reduced cortical bone mass, and greater bone fragility. Treating the Enpp1^asj/asj mice with recombinant Enpp1-Fc protein between weeks 2 and 5 normalized trabecular bone mass, normalized or improved bone biomechanical properties, and prevented the development of nephrocalcinosis and renal failure. The data suggest that conventional ARHR2 therapy does not address low BMD inherent in ENPP1 deficiency, and that ENPP1 enzyme replacement may be effective for correcting low bone mass in ARHR2 patients without increasing the risk of nephrocalcinosis. © 2021 American Society for Bone and Mineral Research (ASBMR).     

Pneumocephalus secondary to colonic perforation by ventriculoperitoneal shunt catheter

We present a case of colonic perforation as a complication arising from ventriculoperitoneal shunt catheter. A 58-year-old woman with a ventriculoperitoneal shunt catheter inserted for obstructive hydrocephalus was admitted to hospital with signs and symptoms of meningitis. CT showed an air-fluid level within both lateral ventricles, raising the possibility of colonic perforation since no other aetiology for the pneumocephalus could be found. The CT demonstration of the colonic perforation played a crucial role in patient management.     

pH-adjusted periocular anaesthesia for primary vitreoretinal surgery

PURPOSE: To evaluate the efficacy of pH-adjusted bupivacaine in conjunction with medial orbital periconal block (periocular anaesthesia). METHODS: Sixty consecutive patients undergoing primary vitreoretinal surgery were enrolled prospectively. RESULTS: Adequate anaesthesia and akinesia with no intraoperative supplementation was achieved in 53 eyes (88.3%). Factors influencing intraoperative supplementation were combined vitrectomy with scleral buckling (p = 0.005) and duration of surgery of more than 2 hours (p = 0.001). No ocular or systemic complication resulted. CONCLUSION: pH-adjusted periocular anaesthesia is safe and effective in patients undergoing primary vitreoretinal surgery.     

Free and esterified fatty acid and cholesterol synthesis in adult males and its effect on the doubly-labelled water method

The purpose of the present study was to estimate whole-body fatty acid and cholesterol synthesis in weight-stable adults and to determine the likely effect on the doubly-labelled water (DLW) method for measuring energy expenditure. Synthesis was measured by 2H incorporation over 14 d in six adult males in approximate energy balance following noradrenaline infusion to maximize mobilization of free fatty acid from adipose tissue. The inter-individual variation in synthesis rates was large and in one subject the proportion of free fatty acid synthesized was ten times that of the mean of the rest of the group; the fasting concentration of esterified fatty acid in this subject was five times that of the rest of the group indicating likely violation of the assumptions underlying the calculation of whole-body synthesis. After 14 d of labelling in the other five subjects, 0.9 (SEM 0.3)% of the circulating free fatty acid, 9.3 (SEM 3.0)% of the esterified fatty acid, 14.6 (SEM 2.4)% of the free cholesterol and 28.3 (SEM 3.7)% of esterified cholesterol had been synthesized de novo. A high rate of synthesis correlated with a low pre-dose 2H abundance both within and between lipid classes suggesting that natural 2H abundance variations in some lipid classes may be used to determine their metabolic origin. Whole-body synthetic rates were 8 g/d for fatty acid and 0.3-0.5 g/d for cholesterol. These values correspond to very small errors on DLW-derived estimates of CO2 production; -2.5 litres/d for fatty acid and -0.1 to -0.2 litres/d for cholesterol. These results, obtained in subjects typically consuming a diet with a lower fat and cholesterol content that the typical Western diet, suggest that the DLW method is unlikely to be affected by fatty acid and cholesterol synthesis in subjects in energy balance consuming a typical Western diet.