After oral intake of drugs, drugs go through the first pass metabolism in the gut and the liver, which greatly affects the final outcome of the drugs' efficacy and side effects. The first pass metabolism is a complex process involving the gut and the liver tissue, with transport and reaction occurring simultaneously at various locations, which makes it difficult to be reproduced in vitro with conventional cell culture systems. In an effort to tackle this challenge, here we have developed a microfluidic gut-liver chip that can reproduce the dynamics of the first pass metabolism. The microfluidic chip consists of two separate layers for gut epithelial cells (Caco-2) and the liver cells (HepG2), and is designed so that drugs go through a sequential absorption in the gut chamber and metabolic reaction in the liver chamber. We fabricated the chip and showed that the two different cell lines can be successfully co-cultured on chip. When the two cells are cultured on chip, changes in the physiological function of Caco-2 and HepG2 cells were noted. The cytochrome P450 metabolic activity of both cells were significantly enhanced, and the absorptive property of Caco-2 cells on chip also changed in response to the presence of flow. Finally, first pass metabolism of a flavonoid, apigenin, was evaluated as a model compound, and co-culture of gut and liver cells on chip resulted in a metabolic profile that is closer to the reported profile than a monoculture of gut cells. This microfluidic gut-liver chip can potentially be a useful platform to study the complex first pass metabolism of drugs in vitro.
Arbutin has been used as a whitening agent in cosmetic products. Melanin, the major pigment that gives color to skin, may be over-produced with sun exposure or in conditions such as melasma or hyperpigmentary diseases. Tyrosinase is a key enzyme that catalyzes melanin synthesis in melanocytes; therefore, inhibitors of the tyrosinase enzyme could be used for cosmetic skin whitening. A recent study has reported that arbutin decreases melanin biosynthesis through the inhibition of tyrosinase activity. However, this inhibitory mechanism of arbutin was not sufficiently demonstrated in skin tissue models. We found that arbutin both inhibits melanin production in B16 cells induced with alpha-MSH and decreases tyrosinase activity in a cell-free system. Furthermore, the hyperpigmentation effects of alpha-MSH were abrogated by the addition of arbutin to brownish guinea pig and human skin tissues. These results suggest that arbutin may be a useful agent for skin whitening.
Enhanced actions or levels of endothelin‐1 (ET‐1), a potent vasoconstrictor, have been associated with decreased blood flow in the retina and peripheral nerves of diabetic animals and may be related to the development of pathologies in these tissues. Hyperglycemia has been postulated to increase ET‐1 secretion in endothelial cells. We have characterized the mechanism by which elevation of glucose is increasing ET‐1 mRNA expression in capillary bovine retinal endothelial cells (BREC) and bovine retinal pericytes (BRPC). Elevation of glucose, but not mannitol, from 5.5 to 25 mmol/l for 3 days increased membranous protein kinase C (PKC) activities and ET‐1 mRNA in parallel levels by 2‐fold in BREC and BRPC. These effects were reversed by decreasing glucose levels to 5.5 mmol/l for an additional 2 days. Glucose‐induced ET‐1 overexpression was inhibited by a general PKC inhibitor, GF109203X, and a mitogen‐activated protein kinase kinase inhibitor, PD98059, but not by wortmannin, a phosphatidylinositol 3‐kinase inhibitor. By immunoblot analysis, PKC‐beta 2 and ‐delta isoforms in BREC were significantly increased relative to other isoforms in the membranous fractions when glucose level was increased. Overexpression of PKC‐beta 1 and ‐delta isoforms but not PKC‐zeta isoform by adenovirus vectors containing the respective cDNA enhanced in parallel PKC activities, proteins, and basal and glucose‐induced ET‐1 mRNA expression by at least 2‐fold. These results showed that enhanced ET‐1 expression induced by hyperglycemia in diabetes is partly due to activation of PKC‐beta and ‐delta isoforms, suggesting that inhibition of these PKC isoforms may prevent early changes in diabetic retinopathy and neuropathy.
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