High-throughput physicochemical and in vitro ADMET screening

During drug discovery, it is important to optimise the affinity for the biomolecular target and also the properties of molecules that influence absorption, distribution, metabolism, excretion, and toxicity (ADMET). The goal is to improve the properties of a lead compound and select highly ‘developable’ candidates. Efficient pharmaceutical property profiling operations are now run in parallel to potency screening during lead optimization and provide data for compound prioritization and for the selection of compounds for in vivo studies. The main components of a profiling strategy suitable for early discovery are the measurement of selected physicochemical properties together with in vitro screening for metabolic stability. In addition, enzyme or cellular assays may be deployed for investigation of cellular permeability (including active and passive transport), plasma protein binding, toxicity, and the potential for drug-drug interactions. The four principal physicochemical parameters measured are lipophilicity, dissociation constant, permeability through artificial membranes, and aqueous solubility. An objective of property-based design is the identification of structure property relationships for ADMET that can suggest structural modifications that will also promote or retain high affinity for the biomolecular target. Sometimes this is not possible and new lead molecules may need to be identified to provide new starting points. A sub-optimal in vitro profile may be acceptable as long as there is a reasonable probability of achieving an adequate in vivo profile for clinical studies. In these cases, the application of composite models that can relate in vitro to in vivo behavior is important. Full ‘physiologically based pharmacokinetic’ (PBPK) models can be used; however, there are also simpler approaches available that may be adequate and more easily applied for ranking compounds within a series. Reliable in vitro—in vivo correlation is still very difficult because of the multiplicity of mechanisms involved. For the future, there is a need to develop better criteria for making mechanistically based classifications to develop differentiated models that are appropriate for different types of compound. It is also difficult to correct models for non-specific binding of drugs to membranes and proteins and we need better lipophilicity measures for accurately estimating the affinity of drugs for tissues. PBPK modeling leads to the exciting concept of the ‘virtual human’; however, PBPK models suitable for drug discovery applications are still in their infancy and it will be some time before their promise is fulfilled.     

Bioethics as care work

German philosopher Martin Heidegger argued that humans are defined by care. The term he used, “Sorge,” picks out a wide range of caring relations, including sorrow, worry, the making of arrangements, and even fending for another. Since coming to The Hastings Center, I've been struck by the genuine care definitive of its scholars’ relationship to their work. Care about newborns, the elderly, and nonhuman animals. Care about doctors, nurses, and health care institutions. Care expressed in the panoply of ways biomedical knowledge and practices inform our havings, doings, and beings in the world. Perhaps in its better moments, bioethics just is care work. But care work is hard and messy.     

Hearing impairment and hypoxia ischaemic encephalopathy: Incidence and associated factors

Objective

To establish the local incidence of hearing loss in newborns with Hypoxic Ischaemic Encephalopathy (HIE) and to identify associated risk factors.

The effect of carbohydrate overfeeding on blood pressure in the pregnant, spontaneously hypertensive rat

Carbohydrate overfeeding increases blood pressure in the spontaneously hypertensive rat. This study was undertaken to determine if dietary carbohydrate supplementation throughout pregnancy could prevent the normal fall in blood pressure during the last week of gestation. Systolic blood pressure in the control-fed pregnant rats decreased progressively during the last week and was in the normotensive range by term; that of the carbohydrate-supplemented, pregnant rats remained high and was not significantly lower than that of nonpregnant rats at any time. At term, daily urinary norepinephrine excretion, but not epinephrine excretion, by the carbohydrate-supplemented pregnant rats was twice that of control-fed nonpregnant and pregnant rats, suggesting that the hypertension was due to increased sympathetic nervous activity. Carbohydrate supplementation had no effect on blood pressure or catecholamine excretion in pregnant, normotensive Wistar-Kyoto rats. There were no differences in litter size or mean birth weight between diet treatment groups of either strain.     

Effects of nutrition and genotype on prion protein (PrPC) gene expression in the fetal and maternal sheep placenta

For placental transmission of scrapie to occur, the normal cellular prion protein (PrPC) must be converted to an abnormal infectious form known as PrPSc. PrPC genotype influences susceptibility to contracting scrapie, but we still do not understand whether genotype or expression levels of PrPC are important in transmission of scrapie. Some evidence exists that nutrition affects expression levels of PrPC. Thus, we evaluated the effects of genotype and nutrition on PrPC mRNA and protein expression in adolescent ewes fed at control (100% of National Research Council [NRC] requirements) or restricted (60% of NRC) levels of diet intake during two periods of pregnancy (days 50-90 and days 90-130)]. Gravid uteri (n=50) from singleton pregnancies were collected at day 130, and placentomes were either separated into caruncular (CAR; maternal) or cotyledonary (COT; fetal) placenta and snap-frozen for PrPC mRNA expression or perfusion fixed for PrPC protein expression. PrPC genotypes were determined (codons 136 and 171) using SNP assay. There were no genotype effects on PrPC mRNA expression in CAR or on PrPC protein expression in either CAR or COT, but PrPC mRNA expression in COT was greater (P<0.02) when codon 136 was homozygous for alanine. Some PrPC protein-positive cells were found in the epithelium of CAR, but most were found in trophoblast binucleate and mononucleate cells of COT. In CAR, from days 90 to 130, PrPC protein abundance was greater (P=0.003) in diet-restricted ewes than in control ewes, but was less uniformly distributed (P<0.007). Additionally, in COT, from days 90 to 130, PrPC protein was less uniformly distributed (P<0.01) in diet-restricted ewes. The localized increase in PrPC protein expression, found in ewes diet-restricted late in pregnancy, may suggest a protective role for PrPC in placental biology. Further study is needed to evaluate whether nutrition, PrPC genotype, and PrPC expression levels influence placental transmission of scrapie.