Risk in innovation: balancing benefits and hazards

Case study: endocrine disruption

Richard M SharpeE-mail: r.sharpe@ed.ac.uk

The Queen’s Medical Research Institute Medical School Main Hospital

Endocrine disruption and human healthAn up-front reality check

Endocrine disruption is responsible for a major portion of human health disorders and is certainly responsible for the changing face of human disease – so-called ‘Western diseases’

Therefore, identifying the causes and preventing them is both desirable and feasible

The big issue is what is causing the endocrine disruption?Is it environmental ‘endocrine disruptors’ or is it other factors related to our modern lifestyle?

Endocrine disruption is all around us

Eating and drinking causes ‘endocrine disruption’

Diet, hormones and getting fatHormone effects of eating ‘high sugar’ foods

So, is sugar an endocrine disruptor?

Eating and drinking causes ‘endocrine disruption’

Increase in visceral (intra-abdominal) fat leads to a decrease in circulating testosterone levels (even in young men)

Relationship between blood testosterone and metabolic syndrome features in adult men

From: Traish et al (2011) Amer J Med 124: 578-587

Endocrine disruptorsDefinition – why the concern

Endocrine disruptors are exogenous substances that alter function(s) of the endocrine system and consequently cause adverse health effects in an intact organism, or its progeny, or (sub)populations

Many man-made chemicals have intrinsic agonistic or antagonistic hormonal activity and may thus affect one or more hormone systems in the body. Examples are: alklyphenols, DDT, certain other pesticides, bisphenol A

A

Other compounds have activities that alter endogenous hormone production within the body. Examples are certain phthalates, azole compounds, bisphenol A

B

The commonest reproductive disorders of the developing and young adult male‘Testicular dysgenesis syndrome (TDS)’

CryptorchidismHypospadias

Testis GC cancerLow sperm countsLow testosterone

? Subnormal

T productionor action

An animal model for human TDS?

• Gestational exposure (E13-E21) of the rat to high doses of certain phthalate esters [eg dibutyl phthalate (DBP) or diethylhexyl phthalate] results in:

Dose-dependent induction of: • Cryptorchidism• Hypospadias• Low testis weight/subfertility• Abnormalities in fetal germ cell development• Suppression of fetal testosterone and Insl3• Reduction in anogenital distance (AGD)

Exposure of pregnant rats to a plasticiser (dibutyl phthalate (DBP; 500mg/kg/day) reduces fetal testosterone

Partly from Scott et al (2008) Endocrinology 149:5820

Control

DBP

Fetal human testis xenograftinginto (castrate male) nude mice

• Grafts grow normally for 6+ weeks

• Treating the host with DBP is thus like experimentally exposing the real human fetal testis

• Can measure testosterone production by the grafts

Exposure of human fetal testis xenografts to 500mg/kg/day DBP has no steroidogenic effects

From Mitchell et al (2012) JCEM 97: E341-E348

Data show Means ± SEM for N=8 fetuses (14-20 weeks’ gestation)Statistical analysis was by paired t test

Xenografts recovered + 6 weeks; hCG treatment from 1-6 weeks

The (ongoing) bisphenol A story

‘Feeding your baby from a polycarbonate milk bottle* is like feeding it a contraceptive pill’ (Fred vom Saal)

*containing bisphenol A, which has weak estrogenic activity

Bisphenol A estrogenicityThe reality

The reality is that you would need thousands of ‘bisphenol A pills’ to match an oral contraceptive pill for estrogenic potency

So what is the ‘truth’ about bisphenol A?Is it an ‘obesogen’?

• We are all exposed

• Our main route (95%) of exposure is dietary (oral)

• Conjugation of BPA occurs rapidly in the body rendering it biologically inactive

• Most measurements of BPA in the body (including exposure) are detecting primarily conjugated BPA

Effect of switching to a fresh food dietfor 3 days on Bisphenol A exposure

From: Rudel et al (2011) Environ Health Perspect 119: 914

So a ‘healthier’ fresh food diet is associated with markedly lower BPA levels.

Such a diet is also clearly associated with lower risk of obesity, type 2 diabetes, cardiovascular disease etc

This is what we suggest as a hypothesis – which requires urgent investigation

RM Sharpe & AJ Drake

Western diet

Obesity, type 2 diabetes etc

Higher bisphenol A exposure

A real endocrine disruptor issue that will not go away

The risk posed by exposure to ‘low level’ combinations of endocrine disruptors

The ‘mixtures’ issue - ‘The cocktail effect’

Effects of perinatal exposure to mixturesof ‘anti-androgenic’ chemicals in rats

Data courtesy of Earl Gray (EPA, USA)

‘Real-world’ exposure to environmentalchemicals: effects on testis development

Ewes reared on pasture fertilized with:

• Conventional fertiliser (= control)

• Sewage sludge* (= treated)

*According to EU recommendations

For ~20 common contaminantsquantified in mothers/fetuses

there was no significant increase in sludge-exposed animals

Adapted from Bellingham et al (2011) Int J Androl doi: 10.1111/j.1365-2605.2011.01234.x

Sperm production in adulthood in sheepafter rearing on control or ‘treated’ pasture

Another case of endocrine disruption?Thank you for your attention