Biofouling and stability of synthetic polymers in sea water

Commercial synthetic polymers namely Polycarbonate (PC), Low density polyethylene (LDPE), High density polyethylene (HDPE), and Polypropylene (PP) coupons were immersed for a period of 12 months (Feb 2006 – Feb 2007) in Bay of Bengal, East coast, India. Samples were retrieved every month and the extent of biofouling and biodegradation were monitored. Biofouling was found to depend not only on the season but also on the chemical nature of the polymer. Surface energy of all the four polymers is positively correlated with fouling only at the initial stages (three months) while surface roughness had a negative correlation. The later increased during the study period. Total suspended solids and organic matter were more abundant on HDPE, followed by PP and LDPE, indicating that among polyolefins hydrophobic surfaces (lower surface energy) favor biofouling over one year. Maximum fouling was observed on polycarbonate during initial three months. Chlorophyll a showed a decreasing trend during the study, as secondary foulers such as Balanus amphitrite, were dominant after the monsoon (6th month in the present study). Maximum weight loss was seen in LDPE (1.9%), followed by that in HDPE (1.6%), PC (0.69%) and finally in PP (0.65%) samples in the 12 months time period. FTIR spectra of PC displayed a decrease in carbonate carbonyl index, while an initial increase and a decrease in carbonyl index of polyolefins as a function of time indicated biodegradation.     

Mechanistic investigations of lipase-catalyzed degradation of polycarbonate in organic solvents

The biodegradation of an engineering thermoplastic, poly (bisphenol-A carbonate) (BPAPC), was carried out using three different lipases from Candida antarctica (CAL), Candida rugosa (CRL) and porcine pancreas (PPL) in water-miscible (tetrahydrofuran) and water-immiscible (chloroform) solvents for 10 days. The degradation was monitored by gel permeation chromatography and Fourier transform infrared spectroscopy. Maximum degradation (ca. 60% reduction in M(n)) of BPAPC was observed in THF with PPL when compared to the control without the enzyme. The degradation products in all the experiments were bisphenol-A and 4-α-cumyl phenol suggesting that the lipases act through an end-chain scission on the polymer. The degradation of BPAPC in THF was in the order of PPL>CAL>CRL, while in CHCl(3) it was CRL>CAL>PPL. To understand this disparity, and to probe the mechanistic aspects of degradation, molecular dynamics investigations were performed on the lipases with model BPAPC in both the solvents. The results also suggested that catalytic triad (Ser, His, Asp/Glu) was involved in the hydrolysis of carbonate bond leading to release of bisphenol-A. These data provide us the basic understanding of the degradation mechanism and a novel methodology for degrading polycarbonate.     

Inducible overexpression of endothelial proNGF as a mouse model to study microvascular dysfunction

Impaired maturation of nerve growth factor precursor (proNGF) and its accumulation has been reported in several neurodegenerative diseases, myocardial infarction and diabetes. To elucidate the direct impact of proNGF accumulation identified the need to create a transgenic model that can express fully mutated cleavage-resistant proNGF. Using Cre-Lox technology, we developed an inducible endothelial-specific proNGF transgenic mouse (proNGF^Loxp) that overexpresses GFP-conjugated cleavage-resistant proNGF123 when crossed with VE-cadherin-CreERT2 (Cre). Expression of proNGF, inflammatory mediators, NGF and VEGF was evaluated by PCR, Western blot and immunohistochemistry. EC-proNGF overexpression was confirmed using colocalization of anti-proNGF within retinal vasculature. EC-proNGF did not cause retinal neurotoxicity or marked glial activation at 4-weeks. Microvascular preparation from Cre-proNGF mice showed significant imbalance of proNGF/NGF ratio, enhanced expression of TNF-α and p75^NTR, and tendency to impair TrkA phosphorylation compared to controls. EC-proNGF overexpression triggered mRNA expression of p75^NTR and inflammatory mediators in both retina and renal cortex compared to controls. EC-proNGF expression induced vascular permeability including breakdown of BRB and albuminuria in the kidney without affecting VEGF level at 4-weeks. Histopathological changes were assessed after 8-weeks and the results showed that EC-proNGF triggered formation of occluded (acellular) capillaries, hall mark of retinal ischemia. EC-proNGF resulted in glomerular enlargement and kidney fibrosis, hall mark of renal dysfunction. We have successfully created an inducible mouse model that can dissect the contribution of autocrine direct action of cleavage-resistant proNGF on systemic microvascular abnormalities in both retina and kidney, major targets for microvascular complication.