The gut microbiome and cardiac surgery an unusual symphony

The relationship between the gut microbiome and various organ systems has gained interest throughout the scientific community in recent times. The understanding of these complex relationships has greatly improved with clinical benefits now being seen. Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation that provides circulatory and respiratory support during cardiac surgery. This physiological support facilitates a still and bloodless field facilitating operations on the heart to be performed. Through various mechanisms CPB results in a systemic inflammatory response syndrome (SIRS). This response can vary from mild hypotension to multiple organ failure. It remains difficult to predict the degree to which a patient will experience SIRS post-operatively. The relationship between the composition of the gut microbiome and inflammatory processes associated with disease has been seen across several fields including gastroenterology, neurology, psychiatry and cardiology. To date, minimal research has been undertaken to examine the impact the gut microbiome has on outcomes following cardiac surgery. This review paper explores the pathophysiology behind the SIRS response associated with CPB for cardiac surgery and the hypothesis that a correlation exists between a patients gut microbiome composition and the degree of inflammatory response experienced following cardiac surgery.

The impact of exogenous nitric oxide during cardiopulmonary bypass for cardiac surgery

OBJECTIVES

Cardiac surgery using cardiopulmonary bypass frequently provokes a systemic inflammatory response syndrome. This can lead to the development of low cardiac output syndrome (LCOS). Both of these can affect morbidity and mortality. This study is a systematic review of the impact of gaseous nitric oxide (gNO), delivered via the cardiopulmonary bypass (CPB) circuit during cardiac surgery, on post-operative outcomes. It aims to summarise the evidence available, to assess the effectiveness of gNO via the CPB circuit on outcomes, and highlight areas of further research needed to develop this hypothesis.

METHODS

A comprehensive search of Pubmed, Embase, Web of Science and the Cochrane Library was performed in May 2020. Only randomised control trials (RCTs) were considered.

RESULTS

Three studies were identified with a total of 274 patients. There was variation in the outcomes measures used across the studies. These studies demonstrate there is evidence that this intervention may contribute towards cardioprotection. Significant reductions in cardiac troponin I (cTnI) levels and lower vasoactive inotrope scores were seen in intervention groups. A high degree of heterogeneity between the studies exists. Meta-analysis of the duration of mechanical ventilation, length of ICU stay and length of hospital stay showed no significant differences.

CONCLUSION

This systematic review explored the findings of three pilot RCTs. Overall the hypothesis that NO delivered via the CPB circuit can provide cardioprotection has been supported by this study. There remains a significant gap in the evidence, further high-quality research is required in both the adult and paediatric populations.

Identification of phenobarbitone-modulated genes in mouse liver by differential display

The molecular basis of how rodent nongenotoxic hepatocarcinogens such as phenobarbitone cause liver-tumor formation is poorly understood. An early effect of phenobarbitone exposure is to induce hepatocyte proliferation transiently, and there is evidence that this may be important for subsequent tumor development. In this investigation, we have used the differential display reverse transcriptase polymerase chain reaction technique to analyze differential gene expression in male C57B1/10J mouse liver during the mitogenic phase of the phenobarbitone response. Seventy-seven putative differentially expressed cDNAs were isolated by differential display, and 13 of them were subsequently confirmed as being differentially expressed (both increased and decreased by phenobarbitone). Seven of the cDNAs were homologous to known mouse or human genes (carboxylesterase, coagulation factor X, amine N-sulphotransferase, human protein disulphide isomerase-related protein, cytochrome c oxidase subunit IV, golgin-245, thioredoxin reductase, betaine-homocysteine methyl transferase) and the remainder were novel. The expression pattern of the sulphotransferase was further characterized, and in mouse liver it was found to be significantly induced by phenobarbitone and not by five other rodent nongenotoxic hepatocarcinogens. In summary, the technique has enabled the identification of previously uncharacterized genes whose expression patterns are differentially altered by phenobarbitone in the mouse liver.

Critical incident stress debriefing in international aid workers

Missionaries are well known to suffer the effects of stress. Patricia Miersma relates missionary stress to combat related stress. 1 Development workers too are known to be at increased risk of death whilst overseas-mostly due to traumatic incidents. Relief workers voluntarily enter high stress situations. These overseas workers are at real risk of Post Traumatic Stress Disorder (PTSD). The issue of Critical Incident Stress Debriefing (CISD, or Psychological Debriefing) has been critically examined in an editorial in the British Medical Journal.3 The first randomized, controlled study of CISD that we are aware of (for motor vehicle accident survivors) was published in 1996.4 With 54 intervention subjects, it did not demonstrate effectiveness.

Point mutation analysis of ras genes in spontaneous and chemically induced C57Bl/10J mouse liver tumours

The high incidence and profile of ras gene mutations reported in spontaneous and chemically induced liver tumours of the B6C3F1 mouse provides a potential means of determining in vivo genotoxicity and its relevance to carcinogenicity. We analysed spontaneous and chemically induced [with 4-amino-biphenyl (ABP), 2-acetylaminofluorene (AAF) and diethylnitrosamine (DEN)] hepatocellular tumours of the C57Bl/10J mouse for H-ras, K-ras and N-ras gene mutations to see if mutational analysis of the ras genes could be useful for such a determination in this strain. Regions of DNA spanning codons 12, 13 and 61 of the ras genes were amplified from formalin fixed liver tumour sections using the polymerase chain reaction. Mutations were detected using allele specific oligonucleotide probing and confirmed by sequencing. We have found that there are few ras mutations in either spontaneous or chemically induced liver tumours in the C57Bl/10J mouse. Out of 25 spontaneous tumours two contained an A to T transversion and one contained an A to G transition in base 2 of H-ras codon 61 and two contained a G to A transition in base 2 of K-ras codon 13 (the K-ras mutations were only faintly detectable and may be present in a subpopulation of the tumour cells). In the case of the 18 ABP induced tumours one contained a C to A transversion in base 1 of H-ras codon 61, and one contained an A to T transversion in base 2 of H-ras codon 61 and one contained a G to C transversion in base 1 of K-ras codon 13. One C to A transversion in base 1 of H-ras codon 61 was detected out of eight AAF induced tumours. Of the 25 DEN induced tumours, one contained an A to G transition and one contained an A to C transversion in base 2 of H-ras codon 61. The data indicate that at least in hepatocellular tumours of the C57Bl/10J strain and using chronic dosing regimes the ras genes do not represent markers for in vivo genotoxic activity.