Could Microplastics Be a Driver for Early Onset Colorectal Cancer?

Abstract

Introduction: The incidence of colorectal cancer in those under 50 years of age (early onset colorectal cancer (EOCRC)) is increasing throughout the world. This has predominantly been an increase in distal colonic and rectal cancers, which are biologically similar to late onset colorectal cancer (LOCRC) but with higher rates of mucinous or signet ring histology, or poorly differentiated cancers. The epidemiology of this change suggests that it is a cohort effect since 1960, and is most likely driven by an environmental cause. We explore the possible role of microplastics as a driver for this change. Review: The development of sporadic colorectal cancer is likely facilitated by the interaction of gut bacteria and the intestinal wall. Normally, a complex layer of luminal mucus provides colonocytes with a level of protection from the effects of these bacteria and their toxins. Plastics were first developed in the early 1900s. After 1945 they became more widely used, with a resultant dramatic increase in plastic pollution and their breakdown to microplastics. Microplastics (MPs) are consumed by humans from an early age and in increasingly large quantities. As MPs pass through the gastrointestinal tract they interact with the normal physiological mechanism of the body, particularly in the colon and rectum, where they may interact with the protective colonic mucus layer. We describe several possible mechanisms of how microplastics may disrupt this mucus layer, thus reducing its protective effect and increasing the likelihood of colorectal cancer. Conclusions: The epidemiology of increase in EOCRC suggests an environmental driver. This increase in EOCRC matches the time sequence in which we could expect to see an effect of rapid increase of MPs in the environment and, as such, we have explored possible mechanisms for this effect. We suggest that it is possible that the MPs damage the barrier integrity of the colonic mucus layer, thus reducing its protective effect. MPs in CRC pathogenesis warrants further investigation. Future directions: Further clarification needs to be sought regarding the interaction between MPs, gut microbiota and the mucus layer. This will need to be modelled in long-term animal studies to better understand how chronic consumption of environmentally-acquired MPs may contribute to an increased risk of colorectal carcinogenesis.

Keywords: colonic mucus layer; colorectal cancer; early onset colorectal cancer; microplastics.

Figure 1

Global plastics production (1950–2015). Plastic production refers to the annual production of polymer resin and fibers. Sources: Ritchie, Hannah, and Max Roser. “Plastic pollution.” Our World in Data (2018) [17]. Copyright 2018, OurWorldInData.org, accessed on 12 June 2023.

Figure 2

Cycle of Microplastics and Human Consumption. MPs are released into the environment as waste products from human consumption (plastic bags, bottles, textiles, tyres, etc.) where they undergo degradation and fragmentation from mechanical forces and UV irradiation. Some MPs are directly consumed by humans through leeching into food and water from food packaging and air pollution. MPs in the environment enter water sources and food supplies (e.g., seafood and livestock), thereby leading to consumption by humans.