Geranic Acid Shows Promise for Reducing UVB Damage and Inflammation in Skin Cells

Researcher's work established an enzyme-based production method and found that the resulting geranic acid reduced several signs of UVB-related injury in laboratory-grown human skin cells.

Sunlight can damage skin at a level that is invisible to the eye, setting off chemical stress inside cells, disrupting their energy systems and activating inflammation. Geranic acid, a naturally occurring compound known for antioxidant, anti-inflammatory and antimicrobial activity, is being investigated for its ability to limit some of that damage. Producing a consistently pure version presents another challenge, because conventional chemical methods can create mixtures that need substantial purification.

Researchers from PROYA Cosmetics Co., Ltd. in Hangzhou, China, brought those questions together in "Enzymatic synthesis of geranic acid and its protective effects against UVB-induced skin photodamage", published in Frontiers in Bioengineering and Biotechnology. Their work established an enzyme-based production method and found that the resulting geranic acid reduced several signs of UVB-related injury in laboratory-grown human skin cells. The findings connect a potentially cleaner manufacturing process with an ingredient that deserves further investigation for skincare applications, with testing in human skin and people still needed.

An enzyme route to high-purity geranic acid

Obtaining geranic acid directly from plants is difficult because natural quantities are small and composition varies, making chemical synthesis the main commercial source. Conventional production can require harsh reagents and generate unwanted byproducts, including mixtures of two molecular forms called cis and trans isomers. The trans form has greater biological activity, giving manufacturers a reason to seek a process that produces it selectively.

The team screened ten candidate geranial dehydrogenase enzymes and selected the most active, designated KDI24_07135. They introduced its gene into Escherichia coli bacteria and used fermentation with continuous nutrient feeding to produce enough enzyme for the reaction. This enzyme converted citral, a starting material containing geranial and neral, into geranic acid.

A second enzyme, NADH oxidase, recycled NAD+, a helper molecule required for the conversion, reducing the need to keep supplying fresh cofactor. This recycling step uses oxygen and produces water, offering an environmental advantage within the reaction system; product purification still required organic solvents.

In a 300-millilitre reaction run for 12 hours at 30°C and pH 8, the researchers reported conversion above 90% and a geranic acid concentration of approximately 15 grams per litre. The purified product had more than 98% trans-isomer purity, with its identity checked using chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy.

Skin cells regain defences against UVB stress

The biological experiments used HaCaT cells, an established laboratory line of human keratinocytes, the cells that make up much of the outer skin layer. Geranic acid showed no obvious toxicity at concentrations up to 250 milligrams per litre over 24 hours, with cell viability remaining above 90%. Researchers selected doses of 62.5, 125 and 250 milligrams per litre for further testing.

Cells received a single UVB exposure of 15 millijoules per square centimetre and were treated with geranic acid immediately afterwards for 24 hours. This timing matters because the experiments examined responses after irradiation, rather than whether the compound physically blocked UVB. The work used at least three independent biological replicates, with vitamin E and dexamethasone serving as reference treatments for oxidative stress and inflammation, respectively.

UVB caused a rise in reactive oxygen species, chemically reactive molecules that can damage cellular components when they accumulate. Geranic acid reduced their buildup in a dose-dependent pattern and lowered malondialdehyde, a marker of damage to fats in cell membranes. It restored the activity of superoxide dismutase and glutathione peroxidase, two enzymes involved in the cells' own antioxidant defences.

The treatment helped preserve the electrical balance across mitochondrial membranes, an indicator of the condition of these cellular energy structures. Medium and high doses produced the clearest improvements, suggesting that the compound's effects extended to an important part of cell function.

Inflammation and damage markers fall after treatment

UVB exposure increased calcium entry into the cells and raised the levels of TRPV1, a channel that allows calcium to pass through cell membranes, and NF-κB, a protein involved in inflammatory signaling. Geranic acid treatment reduced calcium overload and lowered the measured expression of both proteins, accompanied by reduced release of the inflammatory messengers IL-6 and MCP-1. The reductions generally became stronger as the dose increased.

These observations support a possible role for the calcium–TRPV1–NF-κB signaling route in the compound's effects. The experiments do not fully establish how geranic acid acts on that route, so the precise molecular mechanism remains a question for further research.

Researchers found fewer γ-H2AX foci, markers associated with DNA double-strand damage, in treated cells. Levels of p16 and p21, proteins associated with cellular senescence, declined as well. Senescence describes a state in which cells stop dividing and can contribute to tissue dysfunction; changes in these markers suggest reduced cellular stress without establishing that the compound reverses skin ageing.

Geranic acid reduced secretion of MMP-1 and MMP-3, enzymes involved in breaking down the extracellular framework that supports tissues. This finding adds a possible tissue-protection role to the antioxidant and anti-inflammatory results, although the experiment did not measure improvements in wrinkles or skin appearance.

The next steps toward a useful skincare ingredient

The production method offers a practical starting point for making a highly pure ingredient under relatively mild reaction conditions. Increasing output will require more development, because the researchers limited starting-material concentrations to avoid inhibiting the enzymes. A successful small laboratory reaction does not establish the cost, reliability or environmental footprint of commercial manufacturing.

The biological evidence comes entirely from cultured cells, leaving questions about absorption, formulation, irritation and performance in living skin. The authors call for validation in animal models and human skin tissue, alongside closer investigation of the calcium-related inflammatory mechanism. Demonstrating benefits for people would require suitable human testing.

All authors were employed by PROYA Cosmetics, an affiliation disclosed in the paper, and they reported receiving no financial support for the work or publication. The research provides a candidate ingredient and a production approach for further development, with its strongest evidence resting on reduced damage markers in cultured skin cells.