Unraveling the Structure and Function of Melanin through Synthesis.

Melanin is ubiquitous in living organisms across different biological kingdoms of life, making it an important, natural biomaterial. Its presence in nature from microorganisms to higher animals and plants is attributed to the many functions of melanin, including pigmentation, radical scavenging, radiation protection, and thermal regulation. Generally, melanin is classified into five types-eumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelanin-based on the various chemical precursors used in their biosynthesis. Despite its long history of study, the exact chemical makeup of melanin remains unclear, and it moreover has an inherent diversity and complexity of chemical structure, likely including many functions and properties that remain to be identified. Synthetic mimics have begun to play a broader role in unraveling structure and function relationships of natural melanins. In the past decade, polydopamine, which has served as the conventional form of synthetic eumelanin, has dominated the literature on melanin-based materials, while the synthetic analogues of other melanins have received far less attention. In this perspective, we will discuss the synthesis of melanin materials with a special focus beyond polydopamine. We will emphasize efforts to elucidate biosynthetic pathways and structural characterization approaches that can be harnessed to interrogate specific structure-function relationships, including electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. We believe that this timely Perspective will introduce this class of biopolymer to the broader chemistry community, where we hope to stimulate new opportunities in novel, melanin-based poly-functional synthetic materials.

Clinical outcomes of patients with nondiagnostic biopsy during cryoablation of small renal masses.

OBJECTIVE: To compare the outcomes of patients with biopsy-proven renal cell carcinoma (RCC), benign tumors (BTs), and nondiagnostic (ND) biopsies after renal cryoablation (RC). METHODS: We retrospectively reviewed medical records of 114 patients who underwent RC between 2003 and 2013. Patients were stratified according to biopsy histopathology results-RCC, BT, and ND biopsy. We recorded patient demographics and tumor features and examined oncologic outcomes among the 3 groups. RESULTS: RC was performed in 114 patients with 117 tumors. Seventy-two tumors (61.5%) were RCC, 18 (15.4%) were BTs (oncocytoma or angiomyolipoma), and 27 (23.1%) were ND. Patient characteristics and tumor features were similar among the 3 groups. The median follow-up was 26.5, 26.0, and 22.0 months in the RCC, BT, and ND biopsy groups, respectively (P = .18). Residual disease occurred in the RCC (1.4%) and ND biopsy (7.4%) groups, but not in the BT group (P = .19). All 9 patients (12.5%) who developed recurrent disease had biopsy-proven RCC. The 2- and 5-year recurrence-free survival rates (RFS) for patients with biopsy-proven RCC were 90.2% and 81.2%, respectively. Because no patient in the BT and ND biopsy groups had a recurrence, their RFS was 100%. CONCLUSION: No patient with a BT or ND biopsy developed a local recurrence with short-term follow-up, whereas a recurrence developed in 12.5% of biopsy-proven RCC tumors. RFS for patients with biopsy-proven RCC was worse than the other 2 biopsy groups, although not statistically significant. Long-term follow-up in a larger cohort of patients is needed to further evaluate these preliminary findings.