Elevation of plasma levels of L-dopa in transdermal administration of L-dopa-butylester in rats

To increase delivery of L-dopa in its transdermal absorption, a new lipophilic derivative of L-dopa, L-dopa-butylester, was synthesized. An in-vitro study employing two-chamber diffusion cells, in which the excised rat abdominal skin was mounted, revealed that, in the presence of L-menthol and ethanol, L-dopa-butylester penetrated in its original form more effectively than L-dopa. L-Dopa-butylester sheets were made by immersing wiper sheets in methanol containing the compound, and then evaporating the methanol. An extraction study of the compound from the sheets revealed that its stability was maintained for at least 12 weeks. In an in-vivo cutaneous absorption study, an L-dopa-butylester sheet was attached to the shaved rat abdominal skin. A hydrogel containing L-menthol and ethanol was spread on vinyl tape, and this sheet was placed over it. In plasma, the L-dopa level rose linearly between 30 and 180 min after the cutaneous application; L-dopa-butylester was not detected. The L-dopa level was higher than that in which L-dopa was applied. These findings indicated that the lipophilic nature of L-dopa-butylester further increased its penetration through the skin, and that L-dopa-butylester that was taken up into the general circulation system was rapidly converted to L-dopa by hydrolysis in the body.     

Effect of differential processing methods on L-Dopa and protein quality in velvet bean, an underutilized pulse

Different accessions of velvet bean were subjected to traditional and technological processing methods like soaking, germination, microwave cooking, dry heating and γ-irradiation with a view to assess the extent to which the L-Dopa gets reduced. Furthermore, the impact of certain processing methods on the levels of total protein and essential amino acid profiles was also assessed. The percentage of L-Dopa in the raw seeds ranging from 5.63 (Mundanthurai white-coloured) to 4.44 g/100 g DM (Mundanthurai black-coloured). The processes of germination (120 h) and soaking in Ca(OH)₂ solution effected significant reduction in the content of L-Dopa (i.e., from 34.8% to 58.4%; and 5.6% to 54.5%, respectively). On the contrary, dry heat treatment and microwave cooking appeared to be less effective in reducing the contents of the same. While, γ-irradiation at 10 kGy seemed to be more effective in reducing the L-Dopa than at 5 kGy. Soaking in calcium hydroxide, microwave cooking and γ-irradiation had little impact on the profiles of essential amino acids except cystine (which was completely deactivated) in both the accessions of Thachenmalai. Nonetheless, in Thachenmalai (black-coloured) accession upon soaking in calcium hydroxide, the levels of valine, phenylalanine, tyrosine, isoleucine and histidine were found to be comparable with FAO/WHO (1991) requirement pattern. To sum up, of the various processing methods employed in the present study, germination and soaking in calcium hydroxide were effected greater reduction in L-Dopa content and caused minimum effect on the profiles of essential amino acids of seed proteins.     

莲房原花青素对酪氨酸酶活力和黑色素生物合成影响的初步研究

目的：探讨莲房原花青素(LSPC)对酪氨酸酶及其黑色素生物合成的抑制机理。方法：采用酪氨酸酶多巴速率氧化法体外测定药物干预前后酪氨酸酶活性，求出酪氨酸酶抑制率，并作出相应Lineweaver-Burk曲线，推断其抑制类型。结果：莲房原花青素能显著抑制酪氨酸酶活性，其半抑制浓度IC50为1．15g/L。并能有效抑制形成黑色素的中间产物L-多巴色素向黑色素转化其半抑制浓度IC50为1．750g/L。结论 莲房原花青素可抑制酪氨酸酶活性，且属于酪氨酸酶竞争性抑制剂。     

Transdermal absorption of L-dopa from a new system composed of two separate layers of L-dopa and hydrogel in rats

To maintain the stability of L-dopa in hydrogel, a new system composed of two separate layers of L-dopa and hydrogel was developed. L-Dopa sheets were made by immersing L-dopa solution into wiper sheets and by lyophilizing them. Examination for stability of L-dopa in the L-dopa sheet revealed that its stability was maintained for at least 12 weeks, providing the sheet was kept at room temperature in a dark box. In a cutaneous absorption study of L-dopa in rats, an L-dopa sheet was attached to the shaved abdominal skin. A hydrogel composed of cutaneous absorption enhancers, water and ethanol, was spread on vinyl tape (hydrogel sheet), and this sheet was placed over the L-dopa sheet. L-Dopa that was administered transdermally effectively penetrated through the skin: The plasma level of L-dopa peaked at 30 min and remained high between 60 and 180 min after the cutaneous application. Our system, composed of two separated layers of L-dopa and hydrogel, enabled the stability of L-dopa to be maintained without losing transdermal absorption of L-dopa.