Heart failure stimulates colorectal tumour growth through gut microbial alterations of specific populations

Abstract Background/purpose The field of reverse cardio-oncology has received growing attention in the last years, since epidemiological studies showed that patients with HF are at increased risk of developing cancer. In addition, HF can stimulate tumour growth directly in distant organs, including colon cancer. The exact mechanisms underlying this phenomenon, however, remain largely unknown. The connection between the microbiome and colorectal cancer (CRC) has been studied extensively and microbial dysbiosis in CRC is linked to cancer progression. Recent studies have also shown that HF patients display microbial dysbiosis. We hypothesized that microbial dysbiosis might contribute to HF-induced CRC tumour growth. Methods C57BL/6J mice were subjected to myocardial infarction (MI), with sham surgery as control. After six weeks faeces were collected, processed for 16s rRNA sequencing, and pooled for faecal microbial transplantation. CRC tumour growth was provoked in germ-free mice by treating them with Azoxymethane (AOM)/Dextran sodium sulphate (DSS). The CRC mice were transplanted with faeces from MI or sham mice. Disease progression was monitored using the disease severity score and endoscopy. After ten weeks mice were sacrificed, and tumour number and proliferation were quantified. All experimental procedures were performed in accordance with the European Union guidelines (CCD_8141, the Netherlands, LA_1400637, Belgium). Results MI-induced HF resulted in a decrease in microbial diversity (Shannon diversity p=0.018), characterized by a decrease in short chain fatty acid-producing bacteria, including the genera Blautia (p<0.01) and Roseburia (p<0.01). In addition, caecal butyrate levels were decreased in MI mice (p=0.029). These changes were largely comparable to microbial changes observed in HF patients and CRC patients. Interestingly, faecal transplantation with faeces from MI mice resulted in faster growth of CRC tumours in mice treated with AOM/DSS. This was demonstrated by a higher endoscopy score (7.9 ±2.5 vs. 10 ±2.4, p=0.038), indicative of worse disease progression, increased tumour counts (22 ±5.3 vs. 29 ±6, p<0.01), and a higher percentage of Ki67 positive cells in tumour tissue (p=0.012), relative to AOM/DSS treated mice transplanted with faeces from sham mice. Sequencing data revealed several differences in the microbial composition of mice transplanted with faeces from MI mice compared to mice transplanted with faeces from sham mice. Conclusion Our results demonstrate that HF induces microbial dysbiosis in mice. In addition, we show, for the first time, using a faecal transplantation model, that HF-induced microbial dysbiosis is causally involved in CRC tumour growth in a mouse model of CRC. Targeting the microbiome may present a tool to mitigate HF associated co-morbidities, especially cancer.Graphical abstract