Replication viral

Disruption of these defense mechanisms can lead to bacterial colonization or viral infection. Mucus temperature is important in controlling respiratory infections because decreasing below central body core temperature not only impairs ciliary movement,hut also enhances viral replication,- greatly increasing the likelihood of respiratory infection. Drying of airway mucus also increases the possibility of respiratory infection by reducing mucus thickness and impairing mucociliary clearance, i- i--... 

Viruses are small infectious agents composed of a nucleic acid genome (DNA or RNA) encased by structural proteins and in some cases a lipid envelope. They are the causative agents of a number of human infectious diseases, the most important for public health today being acquired immunodeficiency syndrome (AIDS), hepatitis, influenza, measles, and vituses causing diarrhoea (e.g., rotavirus). In addition, certain viruses contribute to the development of cancer. Antiviral drugs inhibit viral replication by specifically targeting viral enzymes or functions and are used to treat specific virus-associated diseases. 

Antiviral Drugs. Figure 1 Basic steps of viral replication (A) binding, (B) entry, (C) genome replication, (D) gene expression, (E) assembly, (F) release. 

Interferon (IFN) differs from bona fide antiviral diugs since it is a natural defense protein of the host organism and does not directly interfere with the viral replication steps. Interferons are small glycoproteins inducing immune modulatory and antiviral activities. They are secreted by lymphocytes, leukocytes and fibroblasts in response to foreign nucleic acids (dsRNA). 

The nonstructural region of the precursor, harboring the viral replication machinery, is cut into its mature components in a maturation reaction in which two viral proteases (NS2-pro and NS3/4A-pro) cooperate. Site-directed mutagenesis of an other wise infectious cDNA has shown that both HCV-encoded proteases are necessary for viral infectivity, but most of the attention has so far been focused on one of them a member of the serine protease family (EC 3.4.21) located in the N-terminal region of the viral NS3 protein. 

Acyclovir (Zovirax) and penciclovir (Denavir) are the only topical antiviral dragp currently available These dragp inhibit viral replication. Acyclovir is used in the treatment of initial episodes of genital herpes, as well as heqies simplex virus infections in immunocompromised patients (patients with an immune system incapable of fighting infection). Penciclovir is used for the treatment of recurrent herpes labialis (cold sores) in adults. 

The requirements of protease inhibitors as drugs in terms of potency, pharmacokinetics, and toxicity will vary depending on the nature of the infection and the goals of therapy. At one extreme is treatment of HlV-1, a chroific infection that requires life-long therapy and full suppression of viral replication. At the other extreme is the treatment of human rhinovirus (i.e., the cold virus), where short-term treatment to blunt viremia will likely be sufficient to reduce the unwanted symptoms of a cold. In all cases, viral proteases represent very attractive targets with familiar mechanisms of catalysis that frequently allow for the design of transition state analogs and with distinct specificities from host proteases. 

CarriUo A, Stewart KD, Sham HL, Norbeck DW, Kohlbrenner WE, Leonard JM, Kempf DJ, Molla A (1998) In vitro selection and characterization of human immunodeficiency virus type 1 variants with increased resistance to ABT-378, a novel protease inhibitor. J Virol 72 7532-7541 Chambers TJ, Nestorowicz A, Amberg SM, Rice CM (1993) Mutagenesis of the yellow fever virus NS2B protein effects on proteolytic processing, NS2B-NS3 complex formation, and viral replication. J Virol 67 6797-6807... 

Viral replication, packaging and release. Drug Disc Today 1 388-397 Meindl P, Tuppy H (1969) 2-Deoxy-2,3-dehydrosialic acids. II. Competitive inhibition of Vibrio cholerae neuraminidase by 2-deoxy-2,3-dehydro-V-acyIneuraminic acids. Hoppe-Seyler s Z Physiol Chem 350 1088-1092... 

Examples of the new generation of NNRTIs are etravirine (TMC125) and rilpivirine (TMC278), with activity against both wild type and resistant viral isolates. Etravirine was approved by the US Food and Drag Administration in lanuary 2008 and is indicated for the treatment of HIV-1 infection in antiretroviral treatment-experienced adult patients who have evidence of viral replication and HIV-1 strains resistant to an NNRTI and other ARV agents. 

Env sequences both temporally and between patients. Two drugs that target HIV-1 entry, enfuvirtide and maraviroc, are now licensed for treatment of HIV-1 infection. The efficacy of these drugs validates entry as a point of intervention in viral hfe cycles and, in the context of HIV treatment, contributes to the growing armamentarium of antivirals which, in multidrug combinations, can effectively inhibit viral replication and prevent disease progression. 

In conclusion, IFNs have proven to be invaluable tools in the fight against chronic viral hepatitis. In these indications, their antiviral properties play a major role and it remains unclear whether their immunomodulatory properties are also important. Disappointing results obtained with purely immunomodulatory molecules, such as interleukins or Toll-like receptor agonists suggest that, if immunomodulation plays any role, potent inhibition of viral replication is also needed. The role of IFNs in the treatment of viral infections other than hepatitis B and C remains elusive. 

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