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Newer Agents for Topical Treatment
Published in Vineet Relhan, Vijay Kumar Garg, Sneha Ghunawat, Khushbu Mahajan, Comprehensive Textbook on Vitiligo, 2020
Devinder Mohan Thappa, Malathi Munisamy
Piperine and its synthetic analogs: Piperine (1-piperoylpiperidine), an alkaloid obtained from black pepper fruit extract, was found to have a stimulatory effect on the growth of cultured melanocytes and induced melanocyte proliferation and dendrite formation in mouse models. However, synthesis of melanin occurred only in the presence of UV radiation. Hence piperine and its analogs, when used for treatment of vitiligo, should be used with concomitant UVA exposure. However, the application of piperine and phototherapy needs to be staggered to avoid photoisomerization [3,6].
Mucocutaneous Side Effects
Published in Ayse Serap Karadag, Berna Aksoy, Lawrence Charles Parish, Retinoids in Dermatology, 2019
Tugba Kevser Uzuncakmak, Ayse Serap Karadag
Retinoid associated photochemical reactions are an issue of concern in several research fields including photochemistry, spectroscopy, and photobiology (35). Such reactions may be classified as photoisomerization, photopolymerization, photooxidation, or photodegradation and may present as photoallergic, photoirritant, and phototoxic clinical responses. The knowledge about the exact mechanism is very limited; however, many patients complain about a decreased tolerance to UV radiation shortly after sun exposure during treatment with retinoids (36). Such photosensitivity is more common with isotretinoin and etretinate and probably is related to the reduction in the thickness of the stratum corneum. Also, the incidence and severity of these reactions are dependent on different factors, including the type of product, vehicle, retinoid concentration, dosage and wavelength of the light, and photoirradiation time (35,36).
Basic Principles in Photomedicine and Photochemistry
Published in Henry W. Lim, Nicholas A. Soter, Clinical Photomedicine, 2018
Cis-trans photoisomerization reactions of cutaneous chromophores appear to be involved in several cutaneous responses to light. Photoisomerization reactions occur in molecules containing at least one carbon–carbon double bond that is not in a ring structure. The cis and trans forms of the molecule interconvert as shown for trans-urocanic acid in Equation 6. Photoisomerization of bilirubin in skin is another example. The visual process is also initiated by a photoisomerization reaction; in this case, the chromophore is retinal rhodopsin, which isomerizes after absorbing visible light. The change in molecular shape that occurs when a molecule changes between cis and trans forms alters the solubility of the molecule or its ability to bind to sites in tissue. Formation of cis-urocanic acid by UVB irradiation of skin is believed to be one of the events for certain photoimmunologic responses (5).
Pharmaceutical strategies for preventing toxicity and promoting antioxidant and anti-inflammatory actions of bilirubin
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Alessio Nocentini, Alessandro Bonardi, Simone Pratesi, Paola Gratteri, Carlo Dani, Claudiu T. Supuran
CN1, the most deleterious form, shows the complete or almost complete absence of UGT1A1 enzyme activity with severe jaundice23,24. Jaundice occurring immediately after birth can be complicated by ABE and KSDs, that, before the introduction of phototherapy and blood exchange transfusion, was fatal in almost all cases or caused serious brain damage with permanent neurologic sequelae. Phototherapy produces the photoisomerization of unconjugated BR biosynthetic (and water-insoluble) form, that is 4Z,15Z-Bilirubin-IX-α, to its water-soluble photoisomers and their successive elimination via bile (Figure 2)11,25,26. The effectiveness of phototherapy decreases gradually with age and patients are at higher risk of sudden brain damage26. New treatments, such as hepatocyte or hepatic progenitor cell transplantation, are been used27. However, liver transplantation is still considered to be the only definitive treatment for CN11,26.
Light mediated drug delivery systems: a review
Published in Journal of Drug Targeting, 2022
The use of nanoparticles to infuse drugs into tumours has demanded even more control over delivery to target sites alongside high precision. From the available options in the electromagnetic spectrum, ultraviolet (UV) and near-infrared (NIR) light are the two most used resources for DDS's. The light uses the advantage of molecules that can undergo photoisomerization, wherein a molecule can be destabilised when exposed to light. For example, liposomes, which are artificial biomimetic substrates with a lipid bilayer, can transport drugs. The lipid bilayer consists of a hydrophilic head and a hydrophobic tail, and the incorporation of a photoisomerizable molecule, such as azobenzene makes the compound vulnerable to light. Upon UV illumination, the lipid bilayer substrate containing azobenzene will change conformation and destabilise, leading to a release in the content [23]. Initially preferred and used UV light lost its ground due to lower penetration depth and risk of damaging DNA and surrounding healthy tissue. While NIR light having a wavelength of 650-900 nm could be easily absorbed by biological tissue and therefore became an epitome for triggering drug release [24,25]. Different techniques, such as two-photon excitation and up-converting nanoparticles using NIR light, photothermal therapy (PTT), and photodynamic therapy (PDT) can be initiated to release the drug systematically. Also, simultaneously releasing heat and triggering the acquittance of singlet oxygen and reactive oxygen species is efficient in killing cancer cells [24,26–28].
New method for the determination of the net bilirubin absorbance in cerebrospinal fluid that minimizes the interference of oxyhaemoglobin and biliverdin
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2020
The estimation of the bilirubin concentration in a solution by spectrophotometric measurement is not a trivial task. The spectrum of a standard solution depends strongly on the buffer and on the procedure employed to prepare it. Solubility and pH are critical conditions and light protection is mandatory in order to minimize bilirubin photoisomerization [8]. A good alternative to assure the solubility of the bilirubin at physiological pH is to use albumin [9] that also mimics the effect of its presence in CSF. The interaction bilirubin-albumin displaces the peak of the bilirubin spectrum to a higher wavelength and with a little increase as well in the height of the peak [10]. Despite the quite variable concentration of proteins in the cerebrospinal fluid, the spectrophotometric properties of the bilirubin in CSF, especially at low concentrations when the precision of its quantitation is more important, are closer to that of a solution with an excess of albumin. The composition of the stock solutions employed in the experiments have double the molar concentration of albumin than bilirubin or biliverdin to assure that there is an excess of albumin in all of the solutions.