You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

The SARS-CoV-2 virus utilizes angiotensin converting enzyme (ACE-2) for cell entry and infection. This enzyme has important functions in the renin-angiotensin aldosterone system to preserve cardiovascular function. In addition to the heart, it is expressed in many tissues including the lung, intestines, brain, and kidney, however, its functions in these organs are mostly unknown. ACE-2 has membrane-bound and soluble forms. Its expression levels are altered in disease states and by a variety of medications. Currently, it is not clear how altered ACE-2 levels influence ACE-2 virulence and relevant complications. In addition, membrane-bound and soluble forms are thought to have different effects. Most work on this topic in the literature is on the SARS-CoV virus that has a high genetic resemblance to SARS-Co-V-2 and also uses ACE-2 enzyme to enter the cell, but with much lower affinity. More recent studies on SARS-CoV-2 are mainly clinical studies aiming at relating the effect of medications that are thought to influence ACE-2 levels, with COVID-19 outcomes for patients under these medications. This review paper aims to summarize what is known about the relationship between ACE-2 levels and SARS-CoV/SARS-CoV-2 virulence under altered ACE-2 expression states.
["Mechanism", "Treatment"]