Tag: uv

A quick look at collagen

KindofStephen

Collagen, you’ve seen it in your skincare products and have probably eaten it at some point (Yay for artificially-coloured and jiggly gelatin). But what is it?

Collagen is composed of a triple helix, three strands of proteins made up of joined amino acids wrapped around each other. The main amino acid constituents of these proteins are glycine, proline, hydroxyproline, lysine, and hydroxylysine. The unique chemical structure of the amino acids helps form the shape and structure that their compounds make.

There are many types of collagen, which differ in their amino acid composition. Type I collagen is the most abundant in the human body, and Type I, III, IV, and others are found in our skin. In our body, multiple strands of collagen are found bundled together in fibrils.

You may have heard that ascorbic acid or Vitamin C is crucial in the formation of collagen, but how? Ascorbic acid is used in the conversion of proline to hydroxyproline along with oxygen, and alpha-ketoglutarate. The reaction is catalyzed or sped up by the enzyme prolyl hydroxylase and an iron. Similarly, it is needed in the hydroxylation of lysine to hydroxylysine by the enzyme lysyl hydroxylase.

Collagens are naturally glycosylated, meaning they have sugar molecules bound to them – they are found attached to the lysine and hydroxylysine molecules by the enzymes galactosyltransferase and glucosyltransferase. While this glycosylation is not fully understood, they seem important in forming and retaining the structure of the collagen. You may have heard of glycation or advanced glycation endproducts (AGEs), this happens when excessive sugar molecules are bound to the collagen non-enzymatically and can affect its structure, function, and flexibility.

The additional -OH (hydroxy) group on the hydroxyproline helps water molecules bind tightly to collagen. The coiled structure of collagen’s triple helix gives it impressive tensile strength and allows it to stretch when forces are applied. When too much force is applied the triple helix structure can become disorganized and damaged, no longer able to return to its triple helix form.

Experiments, where collagen was exposed to UV radiation in vitro, have shown that free radicals generated from the UV energy can cleave or break apart some of the bonds holding the amino acids together. When enough bonds are broken the triple helix structure can no longer be maintained and the collagen fibre loses its shape and function. Adding ascorbic acid to the solution of collagen, when it was exposed to UV, reduced some of the free radicals produced – leading to fewer bonds breaking and structure disruption. This may highlight one of the ways naturally present antioxidants in the skin help us defend against the environment.

N. Metreveli, L. Namicheishvili, K. Jariashvili, G. Mrevlishvili, A. Sionkowska. Mechanisms of the influence of UV irradiation on collagen and collagen-ascorbic acid solutions. International Journal of Photoenergy (2006), DOI: 10.1155/IJP/2006/76830

Duer Research Group. Collagen glycation and diabetes. Website, URL: https://www.ch.cam.ac.uk/group/duer/research/collagen-glycation-and-diabetes

A. Masic, L. Bertinetti, R. Schuetz, S.W. Chang, T.H. Metzger, M.J. Buehler, P. Fratzl. Osmotic pressure induced tensile forces in tendon collagen. Nature Communications (2015), DOI: 10.1038/ncomms6942

J.M. Waller, H.I. Maibach. ge and skin structure and function, a quantitativeapproach (II): protein, glycosaminoglycan, water, andlipid content and structure. Skin Research and Technology (2006), DOI: 10.1111/j.0909-752X.2006.00146.x

Paperview: Evaluation of the protection of a broad-spectrum SPF50+ sunscreen against DNA damage

KindofStephen

Cyclobutane pyrimidine dimers (CPDs) are a form of DNA damage that is caused by UV exposure. CPDs interfere with base pairing during DNA replication – which can lead to mutations and cancer.

UVB radiation is directly absorbed by DNA. The energy causes changes in the bonding of pyrimidine structures found in DNA leading to CPDs and pyrimidine-pyrimidone (6-4) photoproducts.

UVA on the other hand is poorly absorbed by DNA, but was also found to cause CPD formation in human skin. CPDs were found to remain longer in the skin when there was UVA exposure, leading to speculation that UVA may also suppress a repair mechanism.

Our cells do have DNA repair capabilities, where damaged DNA is excised and replaced – but these processes can be overwhelmed by an accumulation of damage.

Experiments have measured the amount of CPD formation in human skin when exposed to UVB. One study found that CPDs were formed even when there was no visible sunburn (0.5 sunburn dose). They also found CPDs in both the epidermis and dermis and these levels were elevated for about 10 days as the skin sloughed off.

These two images from the paper show (A) skin that was not exposed to UVB and (B) skin that was exposed to UVB. The brown staining of the cells indicates presence of CPDs.

The amount of CPDs found in both the epidermis and dermis increased as UVB exposure increased.

A recent experiment performed by Pierre Fabre (manufacturers of Avène) looked at the effect sunscreen had on the  formation of CPDs in human skin after UV exposure.

14 volunteers applied a sunscreen to their forearm and were exposed to UVB and UVA on skin protected by the sunscreen and also on unprotected skin. The area covered in sunscreen received 15 times the dose of UV to cause sunburn, whereas the unprotected skin received 2 times the dose.

After this exposure, their skin was blistered by vacuum and the contents of the blister were examined for CPDs using two different methods: immunostaining and spectrometry (HPLC-MS).

They found that the unprotected skin after exposure to UV had an elevated ratio of CPDs to normal DNA bases (90 CPD to 106 DNA bases). In comparison, the skin protected with the sunscreen had an amount of CPDs similar to unexposed skin and statistically significantly less than the unprotected skin (P < 0.001) – even though the area received more UV exposure. The CPD to normal DNA base ratio was not reported for the sunscreen protected and unexposed skin.

The sunscreen was not named, but it is SPF 50+, broad spectrum, and contained; Tinosorb M and S, Iscotrizinol, Avobenzone, and the antioxidant bis-ethylhexyl-hydroxydimethoxy benzylmalonate.

Preventing the formation of CPDs from reducing UV exposure is the most well-researched option, but there are other newer methods that are emerging – some of which are already available on the market.

Photolyase is a DNA repair enzyme that can be activated by the absorption of a photon and transfer an electron to the CPD, this can separate the CPD back into two normal pyrimidine bases – with the right timing. In humans, the photolyase enzyme no longer works, but there is some evidence that topical application of photolyase may reduce the formation of CPDs. An experiment where photolyase encapsulated in liposomes combined with light exposure was applied to human skin reduced the formation of CPDs by 40%-45% after exposure to UVB.

You can watch a lecture given by Aziz Sanzar about photolyase and DNA repair below. He won the Nobel Prize in Chemistry in 2015 for his work along with his colleagues Tomas Lindahl and Paul Modrich.

S.K. Katiyar, M.S. Matsui, H. Mukhtar, Kinetics of UV light–induced cyclobutane pyrimidine dimers in human skin in vivo: An immunohistochemical analysis of both epidermis and dermis, Photochemistry and Photobiology (2002), DOI: 10.1562/0031-8655(2000)0720788KOULIC2.0.CO2
J. Gwendal, T. Douki, J. Le Digabel, et al, Evaluation of the protection of a broad-spectrum SPF50+ sunscreen against DNA damage, Journal of the American Academy of Dermatology (2018), DOI: 10.1016/j.jaad.2018.05.570

Visualizing how a daily sunscreen can protect the skin from UV damage

KindofStephen

Optical coherence tomography and reflectance confocal microscopy can be used to non-invasively to visualize deep into the skin. Using these techniques we can actually see changes in the structure of the skin and its cells.

This group of researchers with funding from La Roche Posay used the imaging techniques to compare the effect of UVB exposure on skin protected with a high SPF and UVAPF sunscreen and skin that wasn’t protected.

What they found was that doses of UVB that caused long-lasting erythema (redness) caused morphological changes in the skin. Changes observed were spongiosis (abnormal accumulation of fluid), microvesicles, sunburn cells, and blood vessel dilation. None of these were observed in skin that was protected by the sunscreen.

A minimal erythemal dose or MED is the amount of UV energy that causes long-lasting redness in the skin. Just 1 MED was enough to cause morphological changes and 2 caused significantly more. This also relates to SPF. An SPF of 2 would provide enough protection to protect an average population against 2 MEDs.

If reducing your risk of developing skin cancers and preventing photoaging are a goal of yours – this is a great reminder and justification to wear your sunscreen daily!

Antonio Gomes-Neto, Paula Aguilera, Leonor Prieto, Sophie Seité, Dominique Moyal, Cristina Carrera, Josep Malvehy, Susana Puig, Efficacy of a Daily Protective Moisturizer with High UVB and UVA Photoprotection in Decreasing Ultraviolet Damage: Evaluation by Reflectance Confocal Microscopy, Acta Dermato-Venereologica (2018), DOI: 10.2340/00015555-2736

11 research backed tips to get the most out of your sunscreen!

KindofStephen 4 Comments

Now that it’s Spring (though it’s been snowing in Toronto…), I thought I would share some sunscreen tips1 to help you use it better this Spring and coming Summer!

Most people don’t apply enough sunscreen! Across multiple studies people only apply ¼ to ½ the amount needed for the protection on the sunscreen’s label. 2

You may have wondered why the US FDA and other organizations keep the amount needed for SPF testing so high, as it turns out 2.0 mg/cm2 is a bit of a sweet spot when it comes to reproducibility and reliability of the results. 3

Any easy way to help get the amount needed on the skin is to apply your sunscreen twice. Apply a layer, let it dry, then apply a second layer. This method is recommended by the Japanese Ministry of the Environment. 4

Try not to rub your sunscreen too much when you apply it, one study found that vigorous rubbing actually reduced the SPF by 25%. They think it was because the sunscreen was being rubbed off onto the hands. 5

You should wait at least 10 minutes before putting on or taking off clothes, to allow the sunscreen to dry and to prevent the clothing from wiping it off the skin. 6

The WHO recommends reapplying your sunscreen every two hours. Realistically most of us won’t do that, but you should aim to reapply your sunscreen at least once, and especially after physical activity or swimming and bathing. 7

Reapplying your sunscreen just once can reduce your risk of sunburn by 2 to 3 fold! While there’s differing advice on when to reapply, aim to do it at least once throughout the day. 8

One study found that only 60% of the applied sunscreen was still on the skin after 4 hours of wearing clothes, physical activity, and bathing, and only 40% after 8 hours. 9

If you’re on the beach, be aware that sand can remove sunscreen from the skin! Up to 59% could be potentially removed by laying on the sand. 10

Make sure to apply your sunscreen before UV exposure! One study on people on vacation found that they were, on average, getting 100 minutes of UV exposure before they applied their sunscreen! That was almost 30% of the amount needed for a sunburn in some cases. 11

A high SPF sunscreen can help make up for not applying enough. In an experiment, an SPF 100 sunscreen applied “normally” (which is to say, not enough) offered an SPF of 27. 12

…and a bonus tip! While the above animation is super-cute, it’s not super accurate. Sunscreens (both physical and chemical) don’t protect our skin by reflecting and scattering UV energy. Sunscreens attenuate the UV energy, absorbing it and turning it into less harmful energy – most often in the form of heat. Titanium dioxide and zinc oxide do reflect some of the UVA wavelengths, but they reflect much more in visible light spectrum, which is why they can leave a white-cast on the skin – micronization can help reduce this effect! 13

I hope you’ll find these tips helpful this Spring and Summer (and all-year round!), not only does reducing UV exposure slow down extrinsic ageing, hyperpigmentation of the skin, and the formation of broken capillaries, it also reduces our risk of certain types of skin cancers and helps prevent the immune suppression caused by UV – it’s win-win really!