hepatoand reproductive toxicity Flashcards
what is reproductive/ developmental toxicity
any adverse effect on any aspect of male or female sexual structure or function or on the conceptus or lactation, which would interfere w the production or development of normal offspring that could be reared to sexual maturity
reproductive toxicity: effects on sexual behaviour and fertility in males and non pregnant females
developmental toxicity: abnormal structural or functional development following exposure of pregnant or lactating females
teratogenicity: ability to cause gross structural malformations to foetus
describe the function of the placenta
it is a complex organ at the interface between mother and developing foetus; foetal part develops from the chorionic sac, maternal part derives from the endometrium
functions are: gas exchange and transfer of nutrients and waste products, transfer of immunity from mother to foetus (immunoglobulins), secretion of hormones for foetal growth and development
there is normally no mixing of foetal and maternal blood in the placenta
describe placental transfer
general rule of thumb: if a compound in maternal blood is uncharged, has a molecular weight of 1000 or less and not highly bound to proteins then it will cross the placenta
this varies from species to species; species choice is paramount in reproductive toxicity studies
describe placental drug transfer
most drugs will eventually cross the placenta to some extent
this may be beneficial (steroids to aid lung maturation for example) but there is also the possibility that drugs crossing the placenta may cause developmental toxicity or teratogenicity
3 types of drug transfer:
complete (type 1 drugs) e.g thiopental
exceeding (type 2 drugs) e.g ketamine
incomplete, type 3 drugs, e.g suxamethonium
to transfer from mother to foetus a drug must reach the intervillous space and pass through the synctiotrophoblast (outer layer of chorion), the foetal connective tissue and the foetal capillar endothelium
what is DES
diethylstilbestrol
developed in 1938 as an oestrogen mimetic, 5 times more potent than oestradiol
pharmacologically similar to natural oestrogens, therefore deemed safe
prescribed to 2-10 million women between 1941-1971 to prevent miscarriage, 7-8 weeks to prevent miscarriage through progesterone deficiency
later in pregnancy to prevent early labour or to treat breakthrough bleeding
little toxicological assessment performed before being given to women worldwide
in a study of 6000 women who received DES during pregnancy reported that 20% had one or more miscarriages before their first term delivery, compared to 5% in age matched controls
DES did not reduce the incidence of spontaneous abortion, prematurity or postmaturity and may increase premature labour, according to a double blind clinical trial of over 1500 women
DES mothers have an overall increased risk of neoplasia of 10% but an increased risk of developing breast cancer of 30-50%
how did DES effect the daughters
between 1966 and 1969 seven cases of clear cell vaginal adenocarcinoma was seen in young women (15-22) at massachusetts general hospital, this is a very rare disease and usually only seen in elderly
there was a 40 fold risk of CCA for DES daughters compared to general population although this only equates to an incidence of 1.5 per 1000, epidemiological investigation linked this to maternal use of DES during pregnancy
twice risk of developing breast cancer over the age of 40
increased incidence of structural abnormalities of reproductive organs, increased risk of infertility, increased risk of ectopic pregnancy, also increased risk of premature delivery miscarriage and stillbirth
how did DES effect sons
slightly increased risk of testicular cancer observed in some studies
increased risk of CV disease and diabetes as well as osteoporosis
what do animal studies show about DES
the dose doesnt make the poison; DES often more toxic at low conc
in some species DES increased rate of spontaneous abortion
affected sexual differentiation in offspring in several species
offspring of female mice exposed during pregnancy have histological changes in vaginal and cervical epithelial cells, as well as the endometrium, ovary, testis and epididymis
exposure during pregnancy in rats, hamsters, dogs and primates causes tumours
describe DES mechanisms
DES is an exogenous compound that interferes w hormone function; has endocrine disrupting effects
DES undergoes enterohepatic circulation so has relatively long half life (2-3 days)
doesnt appear to be mutagenic (negative in ames test in all strains), but causes chromosome aberrations (aneuploidy), sister chromatid exchange and disrupts mitotic spindles
DES metabolite DES-3’,4’-Q can cause depurinating adducts on DNA, and leads to DNA with apurinic sides leading to error prone base excision repaire leading to mutations
what is thalidomide
discovered in 1953 in west germany
was shown to be an effective sedative and hypnotic in 1957
tests carried out at this time suggested there was no toxicity and no lethal dose was identified, despite no real evidence that it was safe for pregnant women, advertising in 1958 that was sent to thousands of doctors claimed it was safe and good alternative to barbiturates
in 1958 reports started to arise that thalidomide caused peripheral neuritis
was given to treat morning sickness
produced teratogenicity in 100% of foetuses exposed
8000-12000 infants born were affected, less than 50% survived beyond childhood
why did thalidomide cause these adverse reactions
exists as 2 enantiomers
the R(+) enantiomer of thalidomide is a sedative
the S(-) enantiomer of thalidomide was teratogenic
rapid interconversion between the two occurs at physiological pH
how does thalidomide effect limb formation
thalidomide and its analogues inhibit or reduce levels of FgF8 and Shh and can promote cell death in developing limbs
normal limb development;
two key signalling centres; the apical ectoderm
ridge on the distal tip of the bud and the zone of
polarising activity
– These two regions secrete signals that then drive
the limb growth, AER secretes FgF8, which
causes induction of FgF10 from the
mesenchyme and sonic hedgehog from the ZPA.
Shh then causes more FgF8 secretion from the
AER and so limb growth continues, you then
also get activation of Hox genes which help the
patterning of limb growth.
thalidomide causes amelia in cases of prolonged or early exposure leading to total loss of vessels and widespread cell death and all signalling lost
causes phocomelia in cases of short exposure leading to loss of blood vessels, uniform or localised cell death, loss or partial loss of ZPA and AER signalling which later recovers to distalise remaining tissue
does thalidomide produce oxidative stress
thalidomide metabolism may produce oxygen free radicals as well as a free radical oxygen on the metabolite, the oxygen free radical may produce hydrogen peroxide, causing oxadative stress
what are other mechanisms of thalidomide toxicity
DNA intercalation: thalidomide has some structural similarity to adenine and guanine
S-thalidomide fits into the major groove of DNA, however R thalidomide doesnt
soluble guanyl cyclase/NO:
thalidomide can bind to soluble guanyl cyclase
NO promotes angiogensis by stimulating cGMP production
gene expression: thalidomide alters the expression of multiple genes
what is cereblon
possibly the thalidomide binding protein
cereblon forms a ubiquitin ligase and tags certain proteins resulting in their destruction, the cereblon acts as the substrate receptor in this complex
plays a role in the antitumour properties of thalidomide
cereblon through the ligase complex promotes expression of FgF8
thalidomide binds to cereblon and alters the proteins that are tagged
S-thalidomide binds cereblon more strongly than R thalidomide
but transgenic mice that express human cereblon do not exhibit teratogenicity
now thought that binding to cereblon of thalidomide is responsible for the multiple effects (pharmacological and toxicological) of thalidomide and related drugs
what is duane radial ray syndrome
caused by mutations in SALL4 leading to hearing loss, heart and kidney defects, fused spinal bones, lack of a radius, unusually shaped ears, club foot, triphalangeal, absent or extra thumb
SALL4 is important in embryonic development especially in limb development;
SALL4 is a transcription factor which is important in maintaining embryonic stem cells
SALL4 homozygous KOs show early embryonic lethality, heterozygotes resemble DRRS
cereblon, when bound to thalidomide tags SALL4 for destruction, not in all species as there are species differences in SALL4
what type of drugs are now based on the structure of thalidomide
immunomodulatory drugs
describe general hepatotoxicity caused by drugs
drugs are a significant cause of liver injury, drug induced liver injury has been associated with over 1,000 drugs (prescription and over the counter) as well as drugs of abuse and herbal products
drug induced liver injury is the most common reason for a drug to be withdrawn from market (up to 15% of withdrawals due to liver injury)
describe the lobular organisation of the liver
liver roughly arranged in hexagonal lobules
at corners of the lubules is the portal triad containing; a bile duct, hepatic artery (carries oxygenated blood), portal vein (carries deoxygenated blood but also drugs and nutrients)
these drain into the central vein
describe the zones of liver structure
there are 2 zones of liver hepatocytes; zone 1: periportal, zone 2: transitional, zone 3: centrilobular (sometimes pericentral)
oxadative metabolism occurs in zone 1
CYP450 metabolism occurs in zone 3
what are risk factors for drug induced liver injury
age: the elderly population is mostly affected by toxicity of drugs because of physiological changes and polymedication, however, with valproic acid, young patients are the most affected
gender: female patients are often more suscpetible to toxicity of drugs because of biological differences and pharmacokinetics. Sex-specific factors such as menopause, pregnancy and menstruation
alcohol consumption increases risk
drug interactions: co-administration of drugs (or taking herbal remedies)
previous or underlying hepatic diseases
genetic factors: related with genetic polymorphisms in cytochrome P450
bacteria ?: clostridium convert tyrosine and phenylalanine into p-cresol. This undergoes sulphation and increases the likelihood that paracetamol will undergo metabolism via CYP450 instead
describe paracetamol metabolism
90% is metabolised by glucuronidation and sulfation to glucuronide and sulfate metabolites where it is excreted renally
5% undergoes renal excretion unchanged
5% is metabolised by CYP450s (CYP2E1, CYP1A2, CYP3A4) to a reactive metabolite which may or may not react with glutathione: if reacted with glutathione it forms mercapuric acid and cysteine conjugates, if no glutathione reaction it forms hepatotoxic NAPQI
how do CYP450s effect paracetamol metabolism
CYP2E1 and CYP2E1/CYP1A2 KO mice are less sensitive to paracetamol toxicity
but troleandomycin inhibits CYP3A4 and doesnt decrease NAPQI formation in human liver microsomes
what metabolites of paracetamol are toxic
NAPQI binds to hepatic proteins leading to centrilobular necrosis
N-Acetyl-benzosemiquinoneimine free radical binds to renal proteins with damage to kidney medulla
what are stages of paracetamol toxicity
stage 1: non specific symptoms such as anorexia, nausea, vomiting, diaphoresis, may persist for up to 24 hours
stage 2: 24-48 hours after exposure; disturbances in liver function leads to increased levels of AST and ALT, may experience tenderness (upper right quadrant) and liver may be enlarged
stage 3: between 3 and 5 days after exposure:
decreased glycogenolysis and decreased gluconeogenesis lead to hypoglycaemia
increased lipolysis leads to metabolic acidosis
hyperbilirubinaemia
lethargy
increased prothrombin time leads to bleeding
renal failure
hepatic failure
stage 4:
hepatic enzymes levels recover but necrosis persists
what are mechanisms of paracetamol toxicity
the molecular initiating event is the conversion of APAP to NAPQI by CYP2E1 which can then form protein adducts via Pr-SH
cellular responses to molecular initiating event:
increased oxidative stress due to increased hydrogen peroxide, oxygen free radicals etc
impaired energy metabolism: reduced ATP and energy substrate levels
opening of MPTP
impaired oxidative phosphorylation due to inhibition of complexes 1-3 and ATP synthase
DNA fragmentation
sustained increase in cytosolic calcium
organ and organism responses:
necrosis, liver injury, death
how does paracetamol toxicity cause oxidative stress
there is no evidence of formation of reactive oxygen species during the CYP450 metabolism of paracetamol to NAPQI
toxcity is initiated by oxidation of thiol groups on proteins: in a 2 phase model (phase 1 is the metabolic activation of paracetamol and depletion of GSH, phase 2 is no paracetamol present but progressive cell damage seen)
adding methionine or NAC during phase 1 reverses its toxicity
but during phase 2 only NAC reverse toxicity
