In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is back on form and on course to record a decent gain. At the time of writing, the benchmark index is up 0.5% to 8,215.4 points.

Four ASX shares that have failed to follow the market higher today are listed below. Here's why they are falling:

Karoon Energy Ltd (ASX: KAR)

The Karoon Energy share price is down 3% to $1.55. Investors have been selling Karoon Energy and other ASX 200 energy shares today after oil prices sank overnight. According to Bloomberg, the WTI crude oil price was down 4.25% to US$73.87 a barrel and the Brent crude oil price was down 4.25% to US$77.48 a barrel. Traders were taking profit after Israel didn't immediately retaliate against Iran. At the time of writing, the S&P/ASX 200 Energy index is down almost 1.5%.

Mesoblast Ltd (ASX: MSB)

The Mesoblast share price is down 3.5% to $1.41. With no news out of the biotechnology company today, this decline is likely to have been driven by profit taking from some investors. After all, the Mesoblast share price has been on fire in recent weeks. So much so, its shares remain up over 50% since this time last month despite today's weakness. Investors appear to have been buying the company's shares on the belief that the US FDA will give its stem cell therapy the thumbs up in the near future. This follows years of knock-backs from the regulator.

Mineral Resources Ltd (ASX: MIN)

The Mineral Resources share price is down 7% to $47.77. This is despite there being no news out of the mining and mining services company today. However, it is worth noting that most lithium stocks are under pressure on Wednesday. This is possibly due to profit taking after strong gains were recorded in recent weeks. The shares of fellow lithium miners Pilbara Minerals Ltd (ASX: PLS) and Liontown Resources Ltd (ASX: LTR) are both down 3.5% at the time of writing.

Sigma Healthcare Ltd (ASX: SIG)

The Sigma Healthcare share price is down 5% to $1.90. This may also be a case of profit taking. Investors have been bidding the pharmacy chain operator and wholesaler's shares higher after it offered to make court-enforceable undertakings to help get its Chemist Warehouse acquisition over the line. The gains have been so strong that Sigma Healthcare's shares remain up 33% since 30 September despite today's pullback.