Structural Elements Directing G Proteins and ß-Arrestin Interactions with the Human Melatonin Type 2 Receptor Revealed by Natural Variants.

G protein-coupled receptors (GPCRs) can engage distinct subsets of signaling pathways, but the structural determinants of this functional selectivity remain elusive. The naturally occurring genetic variants of GPCRs, selectively affecting different pathways, offer an opportunity to explore this phenomenon. We previously identified 40 coding variants of the MTNR1B gene encoding the melatonin MT2 receptor (MT2). These mutations differently impact the ß-arrestin 2 recruitment, ERK activation, cAMP production, and Gαi1 and Gαz activation. In this study, we combined functional clustering and structural modeling to delineate the molecular features controlling the MT2 functional selectivity. Using non-negative matrix factorization, we analyzed the signaling signatures of the 40 MT2 variants yielding eight clusters defined by unique signaling features and localized in distinct domains of MT2. Using computational homology modeling, we describe how specific mutations can selectively affect the subsets of signaling pathways and offer a proof of principle that natural variants can be used to explore and understand the GPCR functional selectivity.

Human MC4R variants affect endocytosis, trafficking and dimerization revealing multiple cellular mechanisms involved in weight regulation.

The Melanocortin-4 Receptor (MC4R) plays a pivotal role in energy homeostasis. We used human MC4R mutations associated with an increased or decreased risk of obesity to dissect mechanisms that regulate MC4R function. Most obesity-associated mutations impair trafficking to the plasma membrane (PM), whereas obesity-protecting mutations either accelerate recycling to the PM or decrease internalization, resulting in enhanced signaling. MC4R mutations that do not affect canonical Gαs protein-mediated signaling, previously considered to be non-pathogenic, nonetheless disrupt agonist-induced internalization, ß-arrestin recruitment, and/or coupling to Gαs, establishing their causal role in severe obesity. Structural mapping reveals ligand-accessible sites by which MC4R couples to effectors and residues involved in the homodimerization of MC4R, which is disrupted by multiple obesity-associated mutations. Human genetic studies reveal that endocytosis, intracellular trafficking, and homodimerization regulate MC4R function to a level that is physiologically relevant, supporting the development of chaperones, agonists, and allosteric modulators of MC4R for weight loss therapy.

Extended normothermic extracorporeal perfusion of isolated human liver after warm ischaemia: a preliminary report.

BACKGROUND: Donation after circulatory death (DCD) livers are at markedly increased risk of primary graft dysfunction and biliary tract ischaemia. Normothermic extracorporeal liver perfusion (NELP) may increase the ability to transplant DCD livers and may allow their use for artificial extracorporeal liver support of patients with fulminant liver failure. OBJECTIVE: We conducted two proof-of-concept experiments using human livers after DCD to assess the feasibility and functional efficacy of NELP over an extended period. METHODS: We applied extracorporeal membrane oxygenation, parenteral nutrition, separate hepatic artery and portal vein perfusion and physiological perfusion pressures to two livers obtained after DCD. RESULTS: We achieved NELP and evidence of liver function (bile production, paracetamol removal and maintenance of normal lactate levels) in both livers; one for 24 hours and the other for 43 hours. Histological examination showed areas of patchy ischaemia but preserved biliary ducts and canaliculi. CONCLUSIONS: Our experiments justify further investigations of the feasibility and efficacy of extended DCD liver preservation by ex-vivo perfusion.

Normothermic extracorporeal human liver perfusion following donation after cardiac death.

Liver transplantation is a major life-saving procedure and donation after cardiac death (DCD) has increased the pool of potential liver donors. However, livers procured after DCD are at increased risk of primary graft dysfunction and biliary tract ischaemia. Normothermic extracorporeal liver perfusion (NELP) may increase the ability to protect, evaluate and, in future, transplant DCD livers. We conducted a proof-of-concept experiment using a human liver procured by DCD (deemed not suitable for liver donation) to assess the short-term (3 hours) feasibility, histological effects and functional efficacy of NELP. We used an extracorporeal membrane oxygenation circuit with separate hepatic artery and portal vein perfusion to achieve physiological perfusion pressures, and coupled this with parenteral nutrition and an insulin infusion. We achieved NELP with evidence of liver function (bile production, paracetamol removal and control of ammonia, bilirubin and lactate levels) for 3 hours. There was essentially normal liver and biliary tract histology after 8 hours of perfusion. Our experiment justifies further investigation of the feasibility and efficacy of human DCD liver preservation by NELP.

Normothermic extracorporeal perfusion of isolated porcine liver after warm ischaemia: a preliminary report.

Liver transplantation is a major life-saving procedure, and donation after cardiac death (DCD) has increased the pool of potential liver donors. However, DCD livers are at increased risk of primary graft dysfunction and biliary tract ischaemia. Normothermic extracorporeal liver perfusion (NELP) may increase the ability to protect, evaluate and, in future, transplant DCD livers. We conducted proof-of-concept experiments using a DCD model in the pig to assess the short-term (4 hours) feasibility and functional efficacy of NELP. Using extracorporeal membrane oxygenation, parenteral nutrition, separate hepatic artery and portal vein perfusion, and physiological perfusion pressures, we achieved NELP and evidence of function (bile production, paracetamol removal, maintenance of normal ammonia and lactate levels) for 4 hours in pig livers subjected to 15 and 30 minutes of cardiac arrest before explantation. Our experiments justify further investigations of the feasibility and efficacy of human DCD liver preservation by ex-vivo perfusion.

Equity in health care and institutional trust: a communitarian view.

Communitarianism acknowledges and values, and not just instrumentally, the bonds that unite and identify communities. Communitarians also value community per se. This paper argues that trust is likely to be stronger in communities where these bonds are greater. Equity in health care is a social phenomenon. In health care, it is apparent that more communitarian societies, such as Scandinavia and within Aboriginal Australia, are likely to value more equity-orientated systems. Where, as in the latter case, this desire for equity takes place against a background of the powerful dominant (white) society treating the minority (black) society as dependent, Aboriginal trust in Australian society and in its public institutions is eroded. Lack of trust and inequity then come to the fore. This paper discusses institutional trust as a facilitator of equity in health care in the specific context of Indigenous health. The example used is Australian Aboriginal health but the principles would apply to other Indigenous populations as in for example South America.

Equity in health care and institutional trust: a communitarian view

Communitarianism acknowledges and values, and not just instrumentally, the bonds that unite and identify communities. Communitarians also value community per se. This paper argues that trust is likely to be stronger in communities where these bonds are greater. Equity in health care is a social phenomenon. In health care, it is apparent that more communitarian societies, such as Scandinavia and within Aboriginal Australia, are likely to value more equity-orientated systems. Where, as in the latter case, this desire for equity takes place against a background of the powerful dominant (white) society treating the minority (black) society as dependent, Aboriginal trust in Australian society and in its public institutions is eroded. Lack of trust and inequity then come to the fore. This paper discusses institutional trust as a facilitator of equity in health care in the specific context of Indigenous health. The example used is Australian Aboriginal health but the principles would apply to other Indigenous populations as in for example South America.

O comunitarismo reconhece e valoriza (e não apenas no sentido instrumental) os elos que unem as comunidades e com os quais se identificam. Além disso, os comunitaristas também valorizam a comunidade em si. O artigo propõe que a confiança tende a ser maior naquelas comunidades onde os elos são mais sólidos. A eqüidade na assistência à saúde é um fenômeno social. Nos cuidados de saúde, fica evidente que sociedades mais comunitárias, tais como na Escandinávia ou entre os povos aborígines da Austrália, tendem a valorizar sistemas mais orientados para a eqüidade. No caso dos aborígines, o desejo de eqüidade aparece contra o pano de fundo de uma sociedade dominante poderosa (branca) que trata a minoria (negra) como dependente, levando à erosão da confiança dos aborígines na sociedade e nas instituições públicas australianas. Nesse contexto predominam a desconfiança e a falta de eqüidade. O artigo discute a confiança institucional como facilitador da eqüidade na assistência à saúde no contexto específico da saúde indígena. O exemplo utilizado é a saúde dos aborígines australianos, mas os princípios se aplicam a outras populações indígenas, como as da América do Sul.

Equity, by what measure?

Equity has in many instances been framed around the notion of fairness. But the metric used to determine what is fair leaves some people at a disadvantage because the things that they value are not always taken properly into account. If I value mangoes and you value oranges is a measure of fairness based on how many oranges I seek appropriate? If I am expected to give up my love of mangoes in order to get ahead is that fair? The debate about judging equity - about measuring fairness - needs to find the conceptual and methodological space to allow the voices and claims of the other to be heard.

An alternative approach to resource allocation: weighted capacity to benefit plus MESH infrastructure.

This article outlines an approach to resource allocation in healthcare that embraces the concepts of 'capacity to benefit' and management economic social and human (MESH) infrastructure. Health service jurisdictions differ in terms of their capacities to produce benefits for the people they serve. This is for three reasons: (i) some populations already have relatively good health, so the capacity to benefit further is limited compared with others; (ii) even where the health levels of two populations are similar, one population's health problems can be more amenable to health service interventions, i.e. its capacity to benefit from healthcare interventions is greater; and (iii) even where both the health levels and the health problems are similar, one health service may be better placed or better equipped to deliver benefit to its population than the other. In the case of (iii), the capacity to benefit is inhibited because it lacks the necessary MESH infrastructure to deliver health benefits to its population. The approach to resource allocation outlined in this article differs from the more conventional approaches. While resource allocation working party (RAWP)-type formulae concentrate on allocating resources primarily according to the size of the problem (often called heath need and measured in terms of some assessment of the amount of sickness in a population), the starting point with weighted 'capacity to benefit' plus MESH is to ask what good or benefit is sought in allocating resources. In so far as there are variations in the abilities of different authorities by way of MESH, this can result in uneven implementation of health service interventions and consequent inequities and inefficiencies for the relevant populations. There is a need to address this problem of variation through providing support to those jurisdictions that are deficient in these abilities. The building of MESH infrastructure is to be seen as a major plank in any equity strategy, as it may well be the neediest jurisdictions that are most often lacking in MESH. The lack of MESH in these communities will then exacerbate inequities in service delivery.