The role of enteropathy in the pathogenesis of severe acute malnutrition in HIV-infected African children

Globally, malnutrition is a common cause of death in children less than 5 years of age. In Africa, many children who are admitted to hospital with severe malnutrition (termed SAM) have underlying HIV infection. Compared to children who develop SAM because of food shortage, children with HIV and SAM together (termed HIV-SAM) have a higher risk of dying or developing severe infections like blood poisoning (septicaemia), pneumonia or protracted diarrhoea. The reason why the outcome of HIV-SAM is so much worse than SAM alone is not clear. We believe that one important factor may be severe damage to the lining of the gut. Both SAM and HIV target the gut, which becomes inflamed and 'leaky'. Usually harmless bacteria living in the gut are then able to pass across the damaged gut wall into the bloodstream (so-called microbial translocation). Bugs from the gut may therefore cause infections like septicaemia and pneumonia, or may continually stimulate the immune system (a process called inflammation), which may be particularly dangerous in children with malnutrition. We believe that the 'double hit' of HIV and SAM together causes more severe gut damage (termed enteropathy), leading to a higher chance of dying, a lower chance of recovering from malnutrition and a greater risk of infections and inflammation. We plan to recruit 100 children with SAM and 100 children with HIV-SAM from three hospitals in southern Africa (one in Zambia and two in Zimbabwe), to compare the amount of gut damage, microbial translocation and inflammation. These children will be compared to 200 well-nourished children, half of whom are HIV-positive, and half of whom are HIV-negative. We will investigate how damaged, inflamed and leaky the gut is in each group of children, by doing tests on blood, urine and stool samples. In children with SAM and HIV-SAM we will see how acidic the stomach contents are. Stomach acid is a very important barrier against harmful bugs getting into the intestines, and we think the acid may be weaker in children with HIV-SAM, compared to children with SAM. Some children with SAM and HIV-SAM have very protracted diarrhoea and have a high chance of dying, although we do not understand exactly what causes the diarrhoea. By using a small telescope to look inside the gut and take biopsy samples, we can see how damaged the lining of the small intestine (the part of the intestine just beyond the stomach) is, and try to work out exactly what components of the gut wall have been damaged. We will compare microbial translocation between groups by looking for evidence of bacteria, or bits of bacteria, in the bloodstream. We can also look to see if the immune system is being triggered to respond to bugs more in children with HIV-SAM than children with SAM. If we find bacteria in the bloodstream, even at very low levels, we can see whether they have come from the gut by analyzing a sample of stomach juice. We will extract the DNA of any bacteria from the stomach juice, and amplify up the amount to be able to 'read' the sequence of the DNA (like a barcode) to see exactly which bugs are present. We will measure how much the immune system is being stimulated in each group of children, and try to work out if a higher level of inflammation is damaging to the body's metabolism when a child is malnourished. With the very best treatment available at the moment, around 1 in 3 children with HIV-SAM die, and there is an urgent need to find ways of reducing this high mortality. If we show that enteropathy is an important factor, and that it does lead to microbial translocation and inflammation, we could use extra medicines when treating children with HIV-SAM to try to repair the gut wall, stop bugs crossing into the bloodstream, or switch off inflammation, which may improve children's survival.

In sub-Saharan Africa, around one-third of children hospitalized for severe acute malnutrition (SAM) have underlying HIV infection, and HIV has transformed the epidemiology, clinical presentation and outcome of SAM. Mortality in children with HIV and SAM (termed HIV-SAM) is 4-fold higher than in children with SAM alone, for reasons that remain unclear. Both HIV and SAM are characterized by intestinal damage (enteropathy). Intestinal barrier function is critical to health, and loss of this structural and functional barrier enables translocation of intestinal bacteria and proinflammatory molecules to the systemic circulation. We believe that breakdown of the intestinal mucosal barrier is an often-overlooked pathological process underlying SAM, and that the combined impact of HIV and SAM leads to more severe and extensive enteropathy and slower mucosal recover. We will recruit children with SAM HIV-SAM and well-nourished controls from three sites in Zambia and Zimbabwe, to characterize the enteropathy of SAM and HIV-SAM. A longitudinal series of investigations will compare gastric and small intestinal barrier function. In a subgroup with severe symptomatic enteropathy, endoscopy and biopsy will allow detailed assessment of gut architecture, correlation of structure and function, and investigation of the causes of persistent diarrhoea. To investigate the extra-intestinal consequences of enteropathy, we will first compare the microbial composition of the upper gut and plasma using deep sequencing, to determine whether translocation of enteric organisms underlies sepsis and pneumonia in malnourished children; and, second, characterize gene expression profiles to determine whether differences in host inflammatory response underlie the increased morbidity and mortality of HIV-SAM. Overall, this study will provide a rationale for a future trial of interventions to restore mucosal integrity, block microbial translocation and lower chronic inflammation to reduce mortality.

Who will benefit from this research?

There is a recognised critical need for research into HIV-SAM (Heikens et al, Lancet 2008) to better inform clinical management, which remains suboptimal, with mortality rates exceeding 30%. Ultimately, the aim of this study is to better understand the pathophysiology of HIV-SAM to inform changes in clinical management. We therefore anticipate that children with SAM and HIV-SAM, particularly in sub-Saharan Africa where >90% of HIV-infected children live, will be beneficiaries of this research in the longer term. In the short term, the children recruited to this study will receive high-quality clinical care, with additional diagnostic interventions and clinical follow-up in addition to their contribution to research. We plan to share our research findings with families through 'open laboratory' events and design of an interactive science communication tool (discussed in Pathways to Impact). In the UK, our research findings will be disseminated to an estimated 8000 visitors per year to the Centre of the Cell; internationally, our nutrition interactive tool will be available online and since March 2007, the CoC website has had 18.9 million hits, including 640,000 unique hits from 168 countries.

As discussed in the 'Academic Beneficiaries' section, our research is addressing a recognised knowledge gap, and international guideline-setting committees will be engaged in dissemination of these results, and in discussion of plausible future interventions. At national level, we intend to share any relevant clinical results with relevant bodies within the Ministry of Health, such as the Nutrition Cluster of the MoHCW in Zimbabwe.

How will they benefit from this research?

This study will collect unique clinical and biological data on children with SAM and HIV-SAM and we ultimately expect that this work will inform a trial of interventions to improve morbidity and mortality. The outcome of children with SAM after discharge from hospital is not well studied, and we will provide short-term follow-up data that will increase our understanding of outcomes of children beyond acute hospitalisation. Clinician researchers will benefit from new data to characterize the pathophysiology of a frequently encountered, but poorly understood, clinical entity. We expect that data will be published in year 3 of the study (end of 2016) and that this will inform a potential trial, with funding sought in 2017 for a randomized trial of interventions.

Study staff employed on this project will develop new clinical or basic science skills, together with mentoring from investigators and experience in data analysis and publication. There is a critical need to develop scientific capacity in southern Africa to equip a cadre of future researchers to lead important public health research in-country. By linking Zimbabwean and Zambian academic institutions, we hope to strengthen existing links such as the SACORE network to enhance research capability in southern Africa. Researchers studying related conditions, such as schistosomiasis, oral vaccine responses and stunting malnutrition, within our research groups will benefit from discussion of data from this new project, which similarly focuses on enteropathy, and from introduction of new techniques to the labs in each country.