Module 2: Target Tissue Toxicity

what nerves are in the PNS? what are the major subdivisions?

what nerves are in the PNS? what are the major subdivisions?

• cranial & spinal nerves

• somatic (skeletal muscle) & visceral (autonomic)

inorganic Pb toxicity is very dependent on _

• Pb can also pass in the _?

age

• placenta, breast milk, bones

At low Pb concentrations, children can see decreases in:

IQ, Hearing, growth

Lead neurotox history

• known since Roman times

• 1900s: Australia had 1st epidemic of Pb poisoning in children bc of lead paints

• 1970s: widespread subtle cognitive/behavioral deficits in kids exposed to low Pb

Methyl mercury neurotox history

• 1950: in men w/occupational exposure, used as fungicide for beaver pelts

• 1960s: in Japan, mothers contaminated consumed fish → infants were blind, retardation

• 1990: New Zealand & Seychelles, lower doses assoc’d w/dec IQ, memory, attention, language

Thalidomide neurotox history

• in Europe, a pregnant nausea treatment

1950s: congenital limb defects

1970-80: exposure in utero → mental retardation & autism spectrum disorder

neurodevelopment stages

1. proliferation

2. differentiation/migration

3. growth/synaptogenesis & glial fxn/myelination

4. xs neurons are pruned → apoptosis

mechanism of developmental neurotox

• altered cell proliferation, differentiation, or apoptosis

• interference w/neurotransmission

• alteration of morphogenetic process

  • changes in cell shape

• epigenetic (DNA methylation, histone acetylation)

why is timing everything in dev neurotox?

1. later stages dep on success of earlier ones

2. indiv events may be differentially vulnerable to a substance

3. different brain regions develop according to different time lines during pregnancy & postnatal life

   1. ex) alcohol fetal syndrome

4. expression or fxn of neurotoxin targets may vary by dev stage

ex of timing of neurotox

fetal alcohol syndrome

• if early → hypothalamus affected → executive fxn issues

• if later → cerebellum affected → motor fxn issues

glycine receptor alpha-subunit + strychnine

• neonatal isoform is resistant while adult is susceptible

AchE also as a axonal morphogen during dev

• helps guide outgrowth of axon

• OPs target AchE → axon won’t grow right

non-dioxin like (NDL) vs dioxin-like PCBs

NDL PCBs

• more stable, predominate over DL PCBs

• non-coplanar

• don’t bind AhR → but have neurotox via the RyR

DL PCBs

• coplanar

• bind strongly to aryl hydrocarbon receptor (AhR) which regulates dioxin-responsive genes

• similar tox as dioxin (liver, skin, immune)

Ryanodine Receptors (RyR) and NDL PCBs

• fxn?

• types? found where?

• RyR regulates Ca2+ release from ER

• RyR1 = skeletal

• RyR2 = cardiac

• RyR3 = brain

  • all 3 found in brain

  • 1&2 predominate in skeletal and cardiac

how does PCB 95 (NDL-type) exposure lead to behavioral deficits

• learning & memory

• psychomotor

• attention

• normal neurodev: glutamate would enter post-synaptic neuron via NMDAR, AMPAR, or mGluR → depolarization → RyR opens to release Ca2+ → signaling pw triggered → CREB trxn factor → dendrite growth

• PCB 95 binds to RyR → won’t close → xs Ca2+ in cytoplasm → inc Ca2+ oscillations in hippocampal neurons → triggers same pw → xs dendrite growth/spine formation → inc neuronal apoptosis

• proving PCB 95 is RyR dependent

  • PCB 66 (same chem properties as 95) shows no RyR activity

  • siRNA: KO of RyR gene → no arborization

what are the reactions of making ACh and degrading ACh?

choline + acetyl-CoA → ACh + CoA

• via choline acetyltransferase

ACh + H2O → choline + acetate + H2O

• acetylcholinesterase (AChE)

how do SNARE proteins facilitate neurotransmission?

help vesicles of NT fuse w/post-synaptic terminal membrane

• AP arrives to terminal → Ca2+ enters → V- & T-SNARE bind → vesicle of NT fuse w/membrane → NT diffuses to post-synaptic neuron

how do botulinum toxins cause muscle paralysis?

• botulinum (heterodimer) binds to receptor via its heavy chain → vesicle → its light chain leaves vesicle & cleaves SNARE → prevents ACh release

  • reason why botox causes paralysis

what are the 2 hypothesized mechanisms of A-Latrotoxin? This causes what?

1. channel forming: causes xs ACh release by forming a Ca2+ channel in the presynaptic neuron

2. receptor mediated (Latrophilin/CIRL): inc fusion of ACh-vesicles to inc ACh release

• xs ACh → muscle tetany

Uses/Exposures of Organophosphorus Esters (OPs)

• insecticides

• petroleum additives

• plasticizers

• warfare

• pharm

• exposures

  • terrorist/suicide

  • occupational

  • environmental

    • oral, dermal, inhalation

how do OPs cause toxicity? how does this affect autonomic neurochemistry?

target catalytic triad of AChE → ACh accumulation in synapse in …

in somatic NS

• skeletal muscles

in autonomic NS

• parasympathetic: at ganglion synapse

• sympathetic: at ganglion synapse & adrenal medulla

  • → overstimulation of NE and Epi → smooth or cardiac, muscles, glands or GI overstimulated

Acute Cholinergic Crisis effects on PNS and CNS?

• SLUDGE

• DMBBELLS

PNS (muscarinic)

• resp: wheezing, bronchoconstriction

• GI: anorexia, nausea, vomit, diarrhea

• cardio: bradycardia, hypotension

• urinary: incontinence

• glands: hypersalivation, hyperlacrimation, inc xs sweating

• pupils: constricted (miosis), unreactive to light

PNS (nicotinic)

• muscles: fasciculations, twitching, weakness

• sympathetic ganglia: tachycardia, hypertension

CNS

• headache, drowsiness, confusion, blurred vision, slurred speech, ataxia, depression

• lethal: coma, convulsions, respiratory center block

SLUDGE = salivation, lacrimation, urination, diarrhea, GI distress, emesis)

DUMBBELLS = diarrhea, urination, misosis, bronchorrhea, bronchospams, emesis, lacrimation, taxation, sweating)

major classes of neurotoxic chemicals

• natural neurotoxins

• neuroactive drugs

• organic solvents

• metals

• pesticides

• gases

• persistent organic pollutants (POPs)

what are the extraneural factors influencing neurotoxicity?

• sex (endocrine disruptors, P450)

• sp, genotype

• nutrition

  • protein defic → sulfur groups dec needed to detoxify cyanide

  • folate defic → exacerbate MetOH intoxication

• age: the most important factor!

major cell types in NS

1. neuron

2. glial cells: equal # as neurons, support neuron dev, signaling

3. ependymal & endothelial cells: regulate passage b/t brain parenchyma & CSF (ependymal) & blood (endothelial)

glial cell types & role in neurotox

macroglia

• oligodendocytes (myelinating)

• astrocytes (non-myelinating, CYPs, NT uptake)

microglia

• phagocytic cells

• synapse stabilization & elimination/pruning

role in neurotox

• targets for neurotox

• protects neurons

  • facilitates neurotox

how do astrocytes facilitate MPTP toxicity?

• MPTP small, uncharged exits capillary

• MAO-B on astrocyte → MPDP+ now charged → trapped in brain → MPP+

• MPP+ resembles dopamine → interferes w/complex I of mitochondrial ETC → dopaminergic neuron can’t make ATP → neuron dies

VG ion channels are targets for neurotox

• pore blockers

• allosteric modulators that alter gating kinetics

• voltage sensor trapping neurotoxins

• bind for pyrethroid pesticides

mechanism for terminating neurotransmitters in synapse

• reuptake by presynaptic neuron

• enzymatic degradation

• diffusion from synapse

ACh is used where? excitatory or inhibitory NT?

• used by spinal cord neurons to control muscles, brain- memory, autonomic fxn

• excitatory mostly

what are the major inhibitory and excitatory NT in the brain?

GABA = inhibitory

Glutamate (Glut) = excitatory [glutes are exciting]

chemical synapses as targets of neurotox examples

• levodopa: precursor for dopamine

• fenclonine (PCPA) inhibits Tryptophan hydroxylase

• Maneb blocks transport of Glut into vesiscles → inhibit excitatory NT

• Curare: inhibits ACh receptors on skeletal muscle (natives used on arrowheads to paralyze)

• Amitraz: activates autoinhibitory alpha2 NE receptors

• cocaine: inhibits reuptake of dopamine

how can excitotoxicity occur?

1. xs release of Glut or aspartate from presynaptic cells

2. xs stimulation of NMDA, AMPA, or KA (kainate) GlutR by substances other than presynaptic NT

3. dec activity of Glut transporters

4. altered balance of excitatory to inhibitory neurotransmission

   1. inhibit GABA → removes disinhibition of excitability

how does domoic acid (DA, shell fish poisoning) cause excitotoxicity?

DA binds KAR (no DA clearing mechanism) → Na+ influx → overstimulation of NMDAR (req strong depolarization) → Ca/Na+ influx → Ca2+ accumulation → cell death

Ochratoxin A blocks _ to cause excitotoxicty.

glutamate transporter on astrocyte

what level of skin does most toxicity occur at? what are these mature cells called?

epidermis

• squames = full of hydrophobic keratins and lipid envelope out outside

Fick’s Law: penetration through the skin equation

mg absorbed = (hr of exposure)(concentration [cm/hr])(surface area [cm^2])(flux [ug/mL])

• recall: cm^2*cm = cm^3 = mL

what are primary irritants?

cause damage at site of contact via direct chemical or physical action; no prior immunologic sensitization required

allergy mechanism or delayed hypersensitivity

• what are some major allergens?

• what is a hapten?

hapten + tissue protein = complete Ag → sensitized T-lymphocyte

• epoxy resins, Rhus genus of plants, chromates, nickel, rubber chemicals

• hapten = reactive molecules that make protein adducts (complete Ag)

what are some effects on skin from allergic reaction?

• atopic dermatitis

• erythroderma: red skin

• Stevens-Johnson syndrome (dalmatian patches)

• Pyoderma gandrenosum (from tattoo)

• warts (nonsterile tattoo/piercing equipment)

• melanin overproduction

• photodermatitis (lime juice, xs tanning)

• leukoderma (white skin from antioxidant in rubber)

skin whiteners chronic use effects

• cause irregular pigmentation

• commonly have mercury or hydroquinone

  • Hg targets NS, liver, kidneys

  • [papaya poisoning NS, liver, kidneys]

what are the targets for acne and folliculitis?

• what are some acnegenic substances?

acne = sebaceous glands which are blocked → can become cysts by highly chlorinated aromatics → retinoids can’t fix (chloracne)

folliculitis = hair follicle

• cutting oil

t/f: tanning can cause radiodermatitis (atrophy) and skin cancer

true

Arsenic exposure causes _

hyperkeratosis

phototoxicity

immediate rxn resembles sunburn, occurs when agent is stimulated by light to produce radicals

• delayed rxns can result from allergic sensitization when agent is stimulated by light to become covalently attached to protein

petroleum products contain _ that are phototoxic, acnegenic, and carcinogenic (to the skin).

polycyclic aromatic hydrocarbons (PAH)

antioxidants are used where? effects on skin?

• rubber industry

• affect melanocytes → leukoderma

• hydroquinone in whitening soap → Hg tox

thyroid gland anatomy

• basic unit

• which part produces hormone? stores hormone?

• other cell types

• follicle

• follicular cells; colloid

• parafollicular cells (calcitonin → Ca2+ homeostasis)

what are the steps in thyroid hormone (T3/T4) synthesis?

1. Tg is produced in ER & stored in colloid

2. I- uptake via (Na+/I- symporter aka NIS)

3. Thyroperoxidase (TPO)

   1. iodinates tyrosyl residues in Tg

   2. couples MIT & DIT

4. intracellular proteases cleave Tg → releases T4/T3 into blood stream

if low T3/4, what is the pw of the hypothalamic-pituitary-thyroid axis? if high T3/4?

1. HT: low T4/3 signals to brain to release more TRH

2. PG: TRH triggers TSH release

   1. Thyroid: TSH triggers proteolysis of Tg → release of T3/4

3. organs: T3/4 bind to nuclear thyroid receptors in different organs to upregulate gene transcription

• if high T3/4 → inhibit TRH & TSH (- feedback)

at homeostasis which thyroid hormone predominates?

T4 is 80-90% in blood, but T4 → T3 regularly in liver & brain

hypothyroidism

• cause

• symptoms

• most underproduction of T4, reduced I- intake

• hyperplasia → Goiter to compensate for dec efficacy of thyroid gland

• dry hair, puffy face, slow HB, weight gain, constipation, possibly infertility

hyperthyroidism (aka thyrotoxicosis)

• overproduction of T3/4

• speeding up of metabolism

• Graves’ disease (eye bulging), hair loss, goiter, rapid HB, weight loss, diarrhea, menstrual cycle effects

hyper vs hypothyroidism biomarkers

hyper = low TSH, high T4

primary hypo = high TSH, low T4 → thyroid gland issue

secondary hypo = low TSH, low T4 → pituitary gland issue, or tumor/genetic syndromes that prevent PG making TSH

how do PPB affect thyroid hormone biomarkers?

• T3/4 circulates bound to transport proteins

  • globulin >> albumin > TBPA or TTR(=> impt in ex of tox)

• if change levels of these proteins → affects how much T3/4 is measured in blood

perchlorate & thiocyanate affect on thyroid

• both are competitive inhibitors of I- uptake of NIS

  • perchlorate 30x more than I-

  • thiocyanate 15x more than I-

PTU (propylthiouracil) effect on thyroid

competitive binding to TPO → stops iodination rxn → less T3/4 produced → hypothyroidism

hydroxylated PCBs (dielectric and coolant fluids)

competitive binding to TTR (T4 transporter protein to liver)

• xs unbound T4 → signals state of hyperthyroidism to HT/PG → reduced hormone production → hypothyroidism

hydroxylated PBDEs (brominated flame retardants)

• competitive binding to nuclear thyroid hormone receptors → unregulated mRNA & signaling

what are the lungs’ fxn?

• gas exchange - large surface, thin blood-air barrier

• protection

  • air filtration

  • humidification/warming of air

  • metabolism

    • regulates blood content, bioactivation, biosynthesis of mucus

organization of respiratory tract

nasal passage → pharynx → larynx → trachea → main bronchus → bronchiolus → terminal bronchiolus → respiratory bronchiolus → alveoli

respiratory system: humans vs rodents

humans

• simple nasal cavity

• nose/mouth breathers

• more mucous goblet cells, greater # of large airways w/tall epithelial cells & cartilage

• have transitional zone (resp bronchiole)

• 5 lobes- 2 L, 3 R

rodents

• convoluted nasal cavity

• obligate nose breathers

• more Club cells

• no transitional zone (respiratory bronchiole)

• 5 lobes - 1 L, 4 R

conducting airways vs alveoli main cells & fxns

airways

• club cells - secretion, P450 metabolism

• goblet cells - secretion/protection w/mucus

• basal cell - adherence of columnar cells, signaling

• ciliated cells - move mucus lining layer/clearance

alveoli

• type 2 cells - surfactant

• type 1 cells - blood air barrier

which lung cells are progenitor capable & have P450?

progenitors

• club, basal, type 2 cells

P450

• club cells >>> type 2 > macrophages, endothelium

• phase I & II

which airways are supported by cartiginous rings cover by columar epithelium? which are not

trachea & bronchi

not: bronchioles, have smooth muscle, Club cells

alveoli: which cells make the blood air barrier?

on top is surfactant layer (from type 2 cell)

epithelial cell (type I) + basal lamina + capillary endothelial cell

pneumonia

• can be viral or bacteria

• impact depends on lung involvement, treatment, age, history, chemical exposure

  • acute: difficult breathing, fever, high WBC

  • chronic: chronic atelectasis, fibrosis, bronchitis

chronic bronchitis

• conducting airway narrowing

• inflammation of airway wall

• hypersecretion of mucus

emphysema

elastin breakdown → alveolar structure breakdown

asthma

• symptoms

• contributors

• reversible airway hyperresponsiveness caused by constriction of smooth muscle & inflammation of airway wall

• inc in stored/secreted mucus, wheezing, inc inflammation (eosinophils/neutrophils)

• most common childhood illness

• genetics, allergies, environmental exposures

fibrosis

deposition of collagen in process of scar formation in injured lung → assoc’d w/chronic inflammation → stiff lung

chronic obstructive pulmonary disease (COPD)

usual syndrome of advanced lung disease = combo of bronchitis + emphysema + some fibrosis

t/f: lung cancer is the #1 killer of men & women

• causes

true

• radon gas, asbestos, diesel exhaust, industrial chemicals

• 2nd hand smoke

• air pollution

what does FEV1 measure? what is the other primary lung fxn measure?

FEV1 = forced expiratory volume in 1 sec

• FVC

how respiratory disease is diagnosed

key consideration for lung study

• lung is dynamic

  • in vivo changes → P450s mature postnatally as does detox

• lung is multifaceted - main cell types in microenvironments

• lung has substantial sp differences

where does ozone (O3) come from?

factory, cars + volatile org cmpds + sunlight → O3

O3 effects on lung

• high levels → damage ciliated epithelium

• lower levels → oxidant stress & inc inflammation

• repeated exposure → remodel lung w/inflammation, mucous, irritate existing lung disease, dec airway size

napthalene sources

cigarette smoke, mothballs, paint, aerosols, vehicle exhaust, pesticides, tar/oil, fire smoke

napthalene is turned toxic when _?

what detoxifies napthalene?

toxic

• targets Club cells w/CYP2F2 → epoxide → tox

• removing or inhibiting GSH → tox

detox

• inc/upregulation of GSH synthesis → dec tox of napthalene

which vessel type has both for lymph and blood?

• what is the fxn of lymph?

capillaries

• maintain fluid balance, absorbs fats (chylomicrons), provide immune defense

blood flow of heart

O2 rich blood into LA → LV → aorta → systemic → tissues → vena cava → RA → RV → lungs

coronary artery blood supply

LCA & RCA (left/right coronary artery)

• RCA delivers blood to SA & AV nodes → regulate HR

Cardiac Conduction & ECG/EKG

• where is the heartbeat?

P wave = atrial cells depolarize

PR = plateau of atrial muscle APs

QRS complex = ventricular cells depolarize & atrial cells repolarize

ST = plateau of ventricular muscle APs

T wave = ventricular cells repolarize

R peaks to R peaks = one HB

cardiomyocyte AP graph

• what are the stages called?

  • what ICs open/close when?

1. depolarization

2. Na+ ch open, K+ ch close

3. brief repolarization

   1. K+ ch open, Na+ close

4. plateau phase

   1. Ca2+ ch open, K+ close

5. repolarization

   1. Ca2+ close, K+ open

6. refractory period

   1. all channels closed (leaky ch → keep resting potential)

cardiomyocyte depolarization → Ca2+ influx → ?

Ca2+ binds to troponin → actin/myosin binding & power stroke

define:

• heart attack

• myocardial ischemia

• hypertrophy

• heart failure/cardiac arrest/myocardial infarction = pumping failure, lack of tissue perfusion

• dec blood flow to heart; usually caused by atherosclerosis or CAD → myocyte death due to hypoxia

• enlarged cells & inc tissue vol

arrhythmia types = irregular heartbeat

bradycardia = slow HB

tachycardia = fast HB [fast fashion is tachy]

• QT prolongation = can trigger fast, chaotic HB, delayed ventricular repolarization

• Torsades de pointes (twisting of peaks) = form of ventricular tachycardia

• can lead to sudden death

Trastuzumab (Herceptin) mechanism

HER2+ breast cancer → Trastuzumab Ab drug targets receptor Tyr kinase HER2 → Ab binding attracts NK cells

• but ventricular cardiac myocytes also express HER2 → drug binds → cardiomyocyte death

how does cocaine influence cardiomyocytes?

cocaine block funny Na+ ch → reduces depolarization (QRS) → reduces EKG amplitudes → inefficient blood pumping → collapse → myocardial necrosis → death

Di-2-etyylhexy phthalate (DEHP)

• found where?

• main metabolite?

• mechanism

• plasticizer, PVCs

• MEHP

• DEHP/MEHP blocks connexon protein synthesis → gap junctions in electrical cell-cell coupling blocked → conduction velocity slower

what are the specific & nonspecific biomarkers of cardiotox?

specific

• CK-MB (other CK isoforms not unique) = if acute myocardial infarction

• B-type natriuretic peptide - released if MAP too high

• T & I cardiac troponins = inc if myocardial damage

nonspecific

• inc myoglobin in plasma

elimination pathways

1. biliary or fecal (liver & gut)

2. renal or urinary (kidney & bladder)

3. respiratory

4. skin (sweat, tears → incidental)

5. hair/nails/feathers

6. breast milk

nephron: proximal tubule

water, salts, glucose, aa reabsorption (transporters)

urea excretion (diffusion)

nephron: loop of Henle

descending: water reabsorption (aquaporins)

ascending: Na+ reabsorption (transporters)

nephron: distal tubule

ion/mineral reabsorption & secretion (transporters)

nephron: collection duct

water reabsorption (aquaporins)

Renin-Angiotensin-Aldosterone-System (RAAS)

1. renin (from kidney) released if hypoperfusion, low MAP, distal ‘nutrient loss’

2. renin cleave Angiotensinogen (from liver) → Angiotensin I (AT I )

3. ACE (from lungs) cleaves AT I → AT II

4. AT II acts on adrenals → aldosterone → induce vasoconstriction → inc MAP → Na+/H2O retention

acute vs chronic kidney injury/disease

• cause

• diagnosis

AKI = sudden loss of kidney fxn

• renal ischemia, crush injury, inflammation/infection, urinary tract blockage

• inc BUN, creatine, urine output

CKD = permanent loss of kidney fxn

• progressive AKI, cardiovasc disease, diabetes mellitus, hypertension

• inc creatine, BUN, GFR, urinary abnormalities for at least 3 months

20-25% of AKI are from

• drugs

• renal lithiasis (kidney stones) = form when urine concentrates from:

  • calcium oxalate/phosphate (diet- leafy greens)

  • uric acid (fluid imbalance)

  • struvite (infection) = most damaging to hepatocyte, shArp

• renal pyelonephritis (acute kidney infn)

  • UTI eg) E.coli

  • permanent damage of kidney → kidney failure

t/f: kidney disease is reversible

true, if recovery w/in 24-48h

GFR < _% → increase in mortality

• when is dialysis needed?

45%

• at 15% GFR

adaption & repair potential of kidneys

• unilateral nephrectomy & congenital atrophy

  • if 1 kidney bad, the other can inc blood flow (via hormones)

• proliferation after tox

  • tubular epithelial cells via differentiation, proliferation, migration

• induction of protective proteins

  • Metallothionein w/metals (excreted in urine)

  • Stress-protein (HSPs) w/toxicants, anoxia, oxidative stress