26. Hepatitis C Virus Flashcards
(110 cards)
1
Q
how was hepatitis C virus discovered?
A
- blood from ppl with virus
- extract RNA and make cDNA
- express in E. coli
- detected antigen
- cloned antigen to get hepatitis C
2
Q
HCV is responsible for 40-60% of _______
A
HCV is responsible for 40-60% of chronic liver disease and is the leading cause of liver transplant
3
Q
how many people infected with HCV become chronically infected?
A
85%
4
Q
HCV vaccine?
A
no vaccine available –> very diverse virus with diverse sequence
5
Q
is HCV cytopathic?
A
no, it doesn’t kill cells it just forces them to continuously make virus
6
Q
what family of virus is HCV?
A
Flaviviridae
7
Q
how is HCV transmitted (8)? what is the main route?
A
- blood transfusion (MAIN)
- injecting drug use
- high risk sexual activity
- health-care workers
- hemodialysis
- mother-to-child
- household exposures
- cocaine use
8
Q
3 ways to diagnose HCV
A
- Serology
- Viral genome copies
- Degree of liver damage
9
Q
describe serology to diagnose HCV
A
Enzyme immunosorbent assay –> look for anti-HCV antibodies in the blood
positive in >95% of chronically infected patients
10
Q
describe looking at viral genome copies to diagnose HCV
A
qPCR –> look for viral RNA in the blood, sign of active infection
11
Q
how can we assess degree of liver damage?
A
look at serum liver enzymes and fibroscan (liver inflammation/fibrosis)
12
Q
2 consequences of HCV infection
A
- acute hepatitis
- chronic hepatitis
13
Q
what is HCV incubation period for developing acute hepatitis?
A
6-10 weeks
14
Q
what happens to 80% of ppl with acute HCV?
A
80% of ppl with acute HCV will have no symptoms
15
Q
what are 7 symptoms of acute HCV?
A
- pain in upper right quadrant
- anorexia
- abdominal pain
- nausea/vomiting
- fever
- fatigue
- jaundice
16
Q
2 possible results of acute hepatitis
A
- 15% will clear infection
- 85% will develop chronic HCV
17
Q
when is hepatitis considered chronic rather than acute?
A
continuing HCV-related disease without improvement for at least 6 months
18
Q
what percent of ppl with chronic hepatitis have no symptoms?
A
60-80%
19
Q
what is chronic hepatitis?
A
slowly progressing lifelong infection
20
Q
2 outcomes of chronic hepatitis and proportions
A
- cirrhosis and liver failure (10-20%)
- Hepatocellular carcinoma (3-5%)
21
Q
when do clinical symptoms of HCV appear?
A
during liver failure
22
Q
how many years can it take btwn infection and development of serious complications?
A
20 years may elapse between infection and development of serious complications
23
Q
evolution of HCV treatment
A
- IFN
- IFN + PI/NI
- Direct acting antivirals
24
Q
3 direct acting antivirals
A
- Inhibitor of NS3 protease
- Inhibitor of NS5B polymerase
- Inhibitor of NS5A
25
what family is HCV part of?
flavivirus
26
what genus is HCV part of?
hepacivirus
27
is HCV enveloped or naked?
enveloped
28
size of HCV, avg size of capsid
40-80nm, 30nm
29
what is the shape of HCV capsid?
SPHERICAL
30
4 characteristics of HCV genome
1. +ssRNA
2. Monopartite
3. Linear
4. 9.6kb
31
describe the HCV genome
5' UTR has IRES, no cap
3' UTR has folded structures
1 long ORF
32
4 HCV structural proteins
1. C = core
2. E1 = envelope glycoprotein
3. E2 = envelope glycoprotein
4. p7 = ion channel
33
6 non-structural proteins
1. NS2 = autoprotease
2. NS3 = protease/helicase/NTPase
3. 4A = protease co-factor
4. NS4B = membranous web
5. NS5A = RNA replication
6. NS5B = RdRP
34
is the long mRNA cleaved by host or virus proteases?
both
35
what is the role of NS2?
autoprotease that cleaves and releases the N-terminus so NS3 can cleave the other non-structure proteins
36
structure of 5' UTR
6 stem loops, stem loop #4 has start codon
37
structure of 3' UTR
3 stem loops near poly U region
38
HCV life cycle (6)
1. binds receptor on hepatocytes
2. fusion and uncoating
3. translating, processing
4. replication
5. assembly
6. release
39
2 models of lipo-viral particles
1. two-particle model
2. single-particle model
40
3 receptors for HCV entry
1. CD81
2. CLDN-1
3. OCLN
41
3 co-receptors for HCV entry
1. GAGs
2. LDLR
3. SR-BI
42
what play a prominent role in viral entry? how?
lipoproteins via lipoviral particles
43
what type of entry is used by HCV?
clathrin-mediated
44
1st step of HCV when it is in the cell
TRANSLATION
45
is HCV capped? how does it accomplish translation?
not capped --> cap-independent translation accomplished by IRES at the stem loops of 5' UTR
46
describe cap-independent translation
IRES binds 40S subunit of ribosome and uses only eIF2 and eIF3 --> places start codon in P site of ribosome to initiate translation
47
what is miR-122?
acts as a cap to protect HCV from degeneration
48
why is miR-122 needed?
normally, an uncapped 5' end of RNA would be degraded so miR-122 prevents this
49
where does polyprotein processing occur?
occurs within membrane complex --> all proteins remain in membrane, not soluble in cytoplasm
50
what proteins do host proteases cleave?
structural proteins
51
what forms the replication complex? (4)
1. NS3 + NS4A
2. NS4B
3. NS5A
4. NS5B
52
role of NS3 and NS4A
NS3 acts as helicase and NS4A is cofactor for NS3
53
role of NS4B
membrane reorganization
54
3 roles of NS5A
phosphoprotein, RNA replication, and assembly
55
role of NS5B
RdRP
56
where does HCV RNA replication occur?
on membranous webs
57
5 functions of membranous webs
1. physical support
2. compartmentalization
3. protection
4. tethering of RNA from unwinding
5. retention of negative strand
58
where do membranous webs derive from?
ER
59
3 structures that membranous webs derive from?
1. lipid droplets
2. double membrane vesicles
3. multi-membrane vesicles
60
what protein induces membranous webs?
NS4B
61
describe pores at membranous webs
lipid vesicles contain pores that allow transport of HCV RNA in/out --> the pores have nuclear pore components redirected to form pores
62
topology of NS5B
Right hand
63
initiation of RdRP
de novo
64
in vitro, what initiates NS5B?
GTP is the initiating NTP in vitro
65
what does NS5B require for its function?
divalent metal ions
66
describe the replication rate of NS5B and consequence
replication rate = 10^12 particles/day but has no proof-reading activity --> ERROR PRONE, therefore many genetic variants
67
describe virion assembly (3)
1. replicated +RNA in membrane vesicles merges with capsid proteins associated with lipid droplets
2. capsid-bound RNA associates with envelope proteins
3. lipoprotein machinery to bud
68
what type of protein is p7?
viroporin
69
what is a viroporin?
ion channel that promotes pH-mediated maturation AND the release of infectious viral particles from the cell
70
2 indications for HCV treatment?
1. liver disease/liver inflammation
2. presence of HCV RNA in the blood
71
goal of HCV treatment
eliminate detectable viral RNA from the blood
72
what was the first approved HCV therapy?
IFN-alpha injection
73
modified IFN-alpha treatment?
pegylated form which slows elimination so only 1 injection per week is needed
74
why do you need treatment nurses for IFN-alpha?
severe side effects
75
8 side effects of IFN-alpha
1. flu-like symptoms
2. depression
3. anxiety
4. restlessness
5. rashes
6. insomnia
7. loss of appetite
8. anemia
76
what % of patients respond to peg-IFNalpha
30-40% respond to peg-IFNalpha alone
77
what is ribavarin?
synthetic nucleoside that mimics guanosine
78
how does ribavarin work? 3 consequences
pairs with cytidine and uridine
1. Inhibition of IMDPH
2. inhibition of RdRP (weak)
3. RNA mutagenesis
79
7 side effects of ribavarin
1. anemia
2. teratogenic
3. fatigue
4. headache
5. insomnia
6. nausea
7. anorexia
80
efficacy of ribavarin
only a broad antivirial --> not effective against HCV when alone
81
results of ribavarin and peg-IFNalpha given together
50% sustained virological response
but 10-20% don't complete therapy due to side effects
82
3 major classes of direct acting antivirals
1. protease inhibitors
2. NS5A inhibitors
3. polymerase inhibiters
83
2 protease inhibitors
1. boceprevir
2. telaprevir
84
protease inhibitors are used in combination with:
peg-IFNalpha/ribavirin
85
2 problems with protease inhibitors?
1. severe side effects
2. viral resistance can quickly emerge
86
3 types of polymerase inhibitors
1. benzimidazole indole derivatives
2. non-nucleoside analogues
3. nucleoside analogues
87
diff btwn non-nucleoside and nucleoside analogues
non-nucleoside analogues --> don't bind in active site
nucleoside analogues --> bind in active site
88
example of nucleoside analogue
sofosbuvir
89
mechanism of sofosbuvir
U analog --> nucleotide inhibitor leads to chain termination
90
duration of sofosbuvir treatment
12 weeks
91
does sofosbuvir work on multiple types of HCV?
>90% sustained virological response for genotype 1
82% sustained virological response for genotype 4
92
describe sofosbuvir as a prodrug
has protected phosphate group so can easily become NTP
93
sofosbuvir course of treatment
viral load quickly decreases to low level when treatment begins
stop treatment, rebounds with diff sequence that reduces drug potency
94
2 possible mechanisms of NS5A inhibitors?
1. affecting RNA binding
2. protein-protein interactions
95
2 types of NS5A inhibitors
1. daclatasvir
2. ledipasvir
96
does NS5A inhibitor work across specific HCV genotypes or many?
works across many genotypes
97
what gives best results of NS5A inhibitors?
combination therapy of daclatasvir and ledipasvir
98
difference btwn genotype and subtype
genotypes differ by 30-35%
subtypes differ by 10-30%
99
3 implications of HCV being genetically diverse
1. immune response
2. disease progression
3. treatment/drug resistance
100
2 ways that HCV drug resistance occurs
1. viral turnover
2. base variants
101
describe the viral turnover of HCV contributing to genetic diversity
many viruses produced per day + high pol error rate + long genome = diversity
102
how many HCV mutations/day can we expect with single mutation? double mutation?
9x10^9 new genomes/day with 1 mutation
5x10^8 new genomes/day with 2 mutations
103
describe base variants contributing to HCV diversity
each base can mutate to 3 other bases --> on a long genome this is a lot of diversity
104
describe the mixture of HCV populations
HCV exists as a mixture of populations of genetically distinct but closely related virions in every patient --> quasispecies
105
prior to therapy, what happens to most resistant viruses
prior to therapy, most resistant viruses are unfit and undetectable
106
describe the HCV viruses along the course of treatment (3 stages)
1. prior to treatment, start with lots of WT virus
2. WT virus decreases with treatment
3. then non-WT virus increases with treatment
107
why does non-WT virus increase with treatment
virus type is selected based on environment
normally, non-WT virus is low
but treatment will allow non-WT type to survive
108
is HCV curable?
yes --> over 95% SVR and RNA viral episome is eliminated
109
4 reasons HCV is a quasispecies
1. resistant variants to antiviral drugs exist before treatment
2. resistant variants are selected during treatment
3. drug resistance can occur with treatment
4. resistance is CONSEQUENCE of treatment failure (not always the cause)
110
how can treatment failure due to resistance be minimized?
1. use combinations of drugs
2. use drugs with higher barrier to resistance
