Neuropatie tossiche - Docenti.unina.it

Scuola di Specializzazione in Medicina del lavoro
III anno
Neuropatie professionali da solventi ed
altri tossici industriali
M. Manno
Università degli Studi di Napoli Federico
II
Elementi di fisiologia del SNC
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Peso 2%, portata card. 14%, consumo O2 18%
Sopravvivenza all’anossia 60”
Consumo elevato di glucosio
BEE
Struttura complessa
Limitate capacità di compenso funzionale
Lipofilicità (25% del peso secco!)
Lunghi assoni, trasporto assonale
Diversi neurotrasmettitori
Classificazione delle neuropatie
tossiche professionali
• Centrali
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–
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Solfuro di carbonio (CS2)
Solventi (benzene, toluene, xilene)
Alcoli alifatici (metilico, etilico, propilico, ecc.)
Pb, Hg, Mg
CO
Piretroidi
Esteri organofosforici
• Periferiche
–
–
–
–
–
-
N-esano
Pb
Acrilamide
As
CS2
Ossido di etilene
Diagnosi
• Anamnesi
• Obiettività
• Laboratorio
– (indicatori di esposizione e di effetto)
• Test funzionali
– EMG
– Potenziali evocati
– EEG
• Tecniche d’immagine (TAC, PET, RMN)
EMG
• Riduzione velocità di conduzione
motoria
– (danno mielinico)
• Aumento latenze distali
– (danno assonale)
Pb
• Encefalopatia acuta e cronica
– (bambini, vascolare, atrofia nervo ottico)
• Neuropatia periferica
– (motoria, n. radiale, “fa le corna”, solo arti superiori, EMG
alterato, danno mielinico e assonale)
• Colica saturnina
• Sempre associata a elevata piombemia
– (> 120 ug/100 ml)
• Regressione lenta
– (6-12 mesi, chelazione con NaEDTA)
CO
• CO-Hb (dal 20-30% in su, coma a 50%
e morte a 70%, ipossia cerebrale)
• Confusione, letargia, epilessia, coma
• Sintomi circolatori, cardiaci,
respiratori
Hg
• Insonnia, anoressia, sintomi psichici
• Tremore (movimenti coreo-atetosici)
• Elevata mercuriuria (300-600 ug/L)
MeHg (Minamata disease): non di
origine professionale
BTX (benzene, toluene, xilene)
• Assorbimento rapido per inalazione, emivita 48 hr,
eliminaz. fino al 50% x esalazione, 30-50%
metabolismo epatico (induzione enzimatica?), 0,1%
nelle urine immodificato
• Euforia -> depressione, cefalea nausea, vertigini,
atassia, coma
• Aritmie fino a f.v. (sensibilizzazione alle catecolamine
endogene)
CS2
• Sindrome neuropsichica acuta
– (delirio , allucinazioni, suicidio, demenza)
• Intoss. cronica
– (sintomi neurocomport., polineurite, impotenza, visus)
• Polineuropatia assonale (esposizione cronica)
• Danno misto: neurologico-vascolare
• Arteriosclerosi diffusa
– (cardiaca, cerebrale, periferica)
• Danno epatico (inibizione P450)
Neuropatie periferiche
Acrilamide
– Assorbimento inalatorio e cutaneo
– Subdola (parestesie, debolezza musc., alter.
riflessi e sensibilità)
– Effetti centrali (atassia, disartria, disturbi
sess.)
– Assonopatia centripeta (dying back) con
rogonfiamento “a corona di rosario”
– Effetti cutanei (lesioni bollose al palmo mani)
Esteri organofosforici
• Sindrome colinergica acuta (recettori muscarinici,
nicotinici e centrali)
– Scialorrea, rinorrea, bronco-ostru/costrizione,
diarrea,dolori addom., bradicardia (s. muscarinici)
– Fascicolazioni, paralisi diaframm. (s. nicotinici)
– Cefalea, confusione, coma (s. centrali)
• Inibizione AChE centrale ed eritrocitaria > 30-40%
• Terapia: pralidossime e atropina
• Polineuropatia periferica da NTE (danno assonale)
n-Esano (MEK, MnBK)
• Tipica periferica sensitivo-motoria (danno
al SNC dubbio)
• Danno assonale per esposizione cronica
(polineuropatia dei calzaturieri)
• Misura di n-esano ematica o aria espirata o
2,5-esandione nelle urine (metabolita
tossico
Classi di solventi organici (con esempi)
(da White & Proctor, 1997, modificata)
Idrocarburi alifatici (n-esano)
Idrocarburi alogenati (tetracloruro di carbonio)
Alcoli (metanolo)
Idrocarburi ciclici (cicloesano)
Esteri (etil acetato)
Eteri (etil etere)
Nitroidrocarburi (etil nitrato)
Chetoni (acetone, metiletilchetone)
Glicoli (glicole etilenico)
Idrocarburi aromatici (benzene, toluene)
Aldeidi (acetaldeide)
Altri (solfuro di carbonio)
Case report
Due casi di intossicazione letale
acuta
Two workers were found dead in a well
where they were burying barrels containing
solvents and solid chemical waste from a
nearby chemical plant…
Autopsy results
brain
lung
lung
kidney
liver
Laboratory findings
Where was CO coming from?
Remarks
1. High CO-Hb levels are likely to have contributed
significantly to acute DCM neurotoxicity
(bioactivation)
2. CO-Hb may be used as a biomarker of exposure
in subjects exposed to DCM (biomonitoring)
Content
• Role of bioactivation in neurotoxicity
– individual chemicals
– neurotoxicants’ interactions
• Biomonitoring of neurotoxicants
– Biomarkers of exposure, effect, susceptibility
– New biomarkers (CYP)
• Final remarks
Part 1
• Bioactivation of neurotoxicants
A - Bioactivation-dependent
Neurotoxicants
Examples:
• n-Hexane (periferal polyneuropathy)
• OP (periferal polyneuropathy)
• Acrylamide (cell & axon degeneration)
activation
CYP2B
detoxication
Interestingly…
• Liver CYP enzyme inducers (PB)
decrease rather than increase MePA
toxicity!
Why?
OP bioactivation is tissue- and
enzyme-specific
• Metabolic activation of Me-Parathion to
Me-Paraoxon in the brain is likely to be
more relevant for toxicity than activation
in the liver.
• CYP2B, but not CYP1A, may be responsible
for Me-Parathion activation in the brain.
activation
detoxication
B - Bioactivation-independent
Neurotoxicants
Examples:
• Pyrethroids (CNS excitatory neurotoxicity)
• CO, CN (cytotoxic hypoxia)
• Pb (CNS & PNS damage)
CYP
Esterases
Evidence indicating metabolism as a
protecting factor against pyrethroid
neurotoxicity*
• Compounds inhibiting esterases or CYP-dependent
monooxygenases increase pyrethroid toxicity.
• Products of pyrethroid biotransformation exhibit a
lower acute toxicity than the parent compounds.
• Pyrethroids do not accumulate and, in general, have no
chronic toxicity.
* although some pyrethroid metabolites have shown
estrogenic properties in vitro (McCarthy et al., 2006)
C - Neurotoxicants’ interactions
By mechanism:
•
•
•
toxicokinetic
biotransformation
toxicodynamic
By type of effect:
•
•
increased toxicity
decreased toxicity (therapeutic)
detoxication
activation
Acute methanol poisoning
• 1-2 hrs
Dizziness
• 6-24 hrs
Vomiting, abdominal pain,
visual impairment, dispnoea
• 24-72 hrs
Unconsciousness, coma, death
Solvent toxicity
Ocular damage
Acidosis
Methanol bioactivation
Treatment
of acute methanol intoxication
• ethanol i.v. administration
• treatment of acidosis
• dialisis
Inhibition of methanol activation
by ethanol
Part 2
• Biomonitoring of neurotoxicants
,
Use, target organ, mechanism, biomarker(s) and BEI
of some occupational neurotoxicants
Chemical
Use
Target
Mechanism
Biomarker
BEI
(ACGIH 2005)
Pb
Paint, plastic,
batteries
PNS/CNS
Peripheral
neuropathy
with segmental
demyelination
Blood Pb
30 ug/100 mL
n-hexane
Solvent in shoe
manufacturing
PNS/CNS
Axonopathy due to
cross linking
2,5-hexandione
in urine
0,4 mg/L
Hg
Cl production
CNS
Extrapiramidal
syndrome
Blood Hg
Urine Hg
15ug/L
35ug/g creat.
As
Insecticide
PNS/CNS
Encefalopathy
(acute), peripheral
neuropathy
(chronic)
As in urine
35 ug As/L
Mg
Dry battery,
alloys
CNS
Degeneration of
striatum/globus
pallidus
-
-
CS2
Artificial fibres,
laboratory
PNS/CNS
Axonal degen.
(vascular damage)
TTCA in urine
5 mg/g creat.
Use, target organ, mechanism, biomarker(s) and BEI
of some occupational neurotoxicants (2)
Chemical
Use
Target
Mechanism
Biomarker
BEI
(ACGIH
2005)
OP
(Parathion)
Pesticide
CNS
AChE inibhition
p-nitrophenol in
0,5 mg/g
creat.,
(70%)
CO
urine,
(RBC AChE activ.)
Incomplete
combustion
CNS
Cerebral hypoxia
COHb,
CO in expired air
3,5%
COHb,
20 ppm
Minerals
separation
CNS
Cytochrome
oxidase inhib.,
Hypoxia
Thiocyanate in
blood
-
Manufacture
of paper
products
PNS/CNS
Axonal
degeneration
Mercapturic acids
in urine
-
Dry Cleaning
PNS
trigeminal
neuropathy
TCA in urine
TCE in blood
80 mg/L
2 mg/l
Insecticide
PNS/CNS
Sodium channel
block
Ester hydrolysis/
oxid./conjug. prod.s
-
Solvent
CNS
Cerebral hypoxia,
oedema
DCM in urine,
(COHb)
0,3 mg/L
(3.5%)
(DCM metab.)
Cyanide
ACRYLAMIDE
TCE
PYRETHROIDS
DCM
New biomarkers of exposure, effect
and susceptibility to neurotoxicants
• CYP2E1 geno- and phenotype as new potential
biomarkers in subjects exposed to neurotoxicants
Apoprotein, haem and substrate in a CYP structure
Protocol of CYP2E1 phenotyping
in vivo by the CHZ test
• no alcohol for 3 days before test
• overnight fasting
• time 0: 500 mg Chlorzoxazone p.o.
• after 2 hrs: Blood sampling and serum storage
• h.p.l.c. analysis and 6-OH-CHZ to CHZ ratio
calculation
+ ethanol
- ethanol
1.
CYP2E1 phenotype as a biomarker
of exposure (or effect?) to
neurotoxicants
• CYP2E1 enzymatic activity inhbition in
vivo in subjects exposed to a mixture of
neurotoxic solvents
+ solvents
2.
CYP2E1 mRNA as a biomarker of
effect by neurotoxicants
• CYP2E1 mRNA expression was assessed in
vivo in subjects exposed to toluene
Environmental Health Perspectives Volume 114, Number 4,
April 2006
Occupational Toluene Exposure Induces
Cytochrome P450 2E1 mRNA Expression in
Peripheral Lymphocytes
Ania Mendoza-Cantú, Fabiola Castorena-Torres, Mario Bermúdez de León,
Bulmaro Cisneros, Lizbeth López-Carrillo, Aurora E. Rojas-García, Alberto
Aguilar-Salinas, Maurizio Manno, and Arnulfo Albores
AIM OF THE STUDY
The effects of occupational exposure to toluene on
the induction of CYP2E1 were investigated in workers
of the printing industry by measuring:
a) CYP2E1 mRNA expression in peripheral lymphocytes
and
b) the 6-OH-CHZ/CHZ metabolic ratio
Expected sequence of events following
toluene exposure
Toluene Exposure
CYP2E1 mRNA expression
CYP2E1 enzymatic activity
(CHZ metabolic ratio)
Preliminary conclusions
from the toluene study
• CYP2E1 mRNA expression in lymphocytes, but not
CYP 2E1 activity in vivo (CHZ ratio), may be a
promising biomarker of effect in workers
exposed to low, but not very low, levels of
toluene.
• CYP 2E1 activity was correlated with hippuric
acid levels in urine but not with CYP mRNA
expression in lymphocytes.
• The relationship between mRNA expression and
CYP 2E1 activity remains to be clarified.
Possible reasons for the lack of
correlation between mRNA expression and
CYP2E1 enzymatic activity (CHZ ratio)
• mRNA expression not effective for new
enzyme synthesis
• other individual factors may affect
enzyme activity (genotype, diet, etc.)
• coexposure to other CYP2E1 substrates
3.
CYP2E1 genotype as a biomarker of
susceptibility to neurotoxicants
• CYP2E1 DRA polymorphism omozygote
genotype in subjects exposed to n-hexane
CYP2E1 polymorphism may be an important
susceptibility factor in n-hexane toxicity
Biomarkers, 11: 65-69, 2006
“Association between metabolic gene polymorphisms
and susceptibility to peripheral nerve damage in
workers exposed to n-hexane: a preliminary study.”
Zhang Y, Liu Q, Liu Q, Duan H, Cheng J, Jiang S, Huang X*, Leng S, He F,
Zheng Y.
National Institute for Occupational Health and Poison Control, Chinese Centre for
Disease Control and Prevention, Beijing, China.
*Shenzhen Institute of Health Inspection, Shenzhen, China
Distribution of CYP2E1 Dra homozygous mutations in
workers exposed to n-hexane in a printing factory
and with (Cases) or without (Controls) periferal
polyneuropathy symptoms
Genotype
Cases
(CYP2E1 Dra
polymorphism)
(n =22)
Homozygotes
18,2 %
(n = 163)
Statistical
significance
3,7 %
p = 0.015
Controls
Should homozygotes for CYP2E1 Dra polymorphism
be prevented from exposure to n-hexane?
Valutazione clinica in caso di sospetta
neurotossicità da solventi
(da White & Proctor, 1997, modificata)
1. Questionario o anamnesi
– storia lavorativa (qualitativa)
– descrizione dell’esposizione (quali-quantitativa)
– Sintomi
2. Esame clinico
– esame neurologico generale (SNC e SNP)
– valutazione di specifiche funzioni sensitivo-motorie e dei riflessi
3. Esami neurofisiologici e radiologici
–
–
–
–
–
–
conduzione nervosa
elettromielogramma
potenziali evocati
PET
TAC
risonanza magnetica
4. Test neurocomportamentali
– funzione cognitiva
– funzione motoria
– umore e personalità
Diagnosi eziologica in caso di sospetta
neurotossicità cronica da solventi
1. Segni, sintomi ed esami funzionali
compatibili con neuropatia da solventi
2. Esposizione documentata e significativa a
solventi neurotossici
3. Assenza di altre patologie o fattori di
rischio
Final remarks
Understanding the pathways of neurotoxicants’
bioactivation may be important:
• to understand their mechanism of action
• to perform a more rational biological monitoring
• to treat and prevent their clinical effects
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