Sungmun Lee

Role of aggregation conditions in structure, stability, and toxicity of intermediates in the Aβ fibril formation pathway

β‐amyloid peptide (Aβ) is one of the main protein components of senile plaques associated with Alzheimers disease (AD). Aβ readily aggregates to forms fibrils and other aggregated species that have been shown to be toxic in a number of studies. In particular, soluble oligomeric forms are closely related to neurotoxicity. However, the relationship between neurotoxicity and the size of Aβ aggregates or oligomers is still under investigation. In this article, we show that different Aβ incubation conditions in vitro can affect the rate of Aβ fibril formation, the conformation and stability of intermediates in the aggregation pathway, and toxicity of aggregated species formed. When gently agitated, Aβ aggregates faster than Aβ prepared under quiescent conditions, forming fibrils. The morphology of fibrils formed at the end of aggregation with or without agitation, as observed in electron micrographs, is somewhat different. Interestingly, intermediates or oligomers formed during Aβ aggregation differ greatly under agitated and quiescent conditions. Unfolding studies in guanidine hydrochloride indicate that fibrils formed under quiescent conditions are more stable to unfolding in detergent than aggregation associated oligomers or Aβ fibrils formed with agitation. In addition, Aβ fibrils formed under quiescent conditions were less toxic to differentiated SH‐SY5Y cells than the Aβ aggregation associated oligomers or fibrils formed with agitation. These results highlight differences between Aβ aggregation intermediates formed under different conditions and provide insight into the structure and stability of toxic Aβ oligomers.

Hsp20, a novel α-crystallin, prevents Aβ fibril formation and toxicity

β‐Amyloid (Aβ) is a major protein component of senile plaques in Alzheimers disease, and is neurotoxic when aggregated. The size of aggregated Aβ responsible for the observed neurotoxicity and the mechanism of aggregation are still under investigation; however, prevention of Aβ aggregation still holds promise as a means to reduce Aβ neurotoxicity. In research presented here, we show that Hsp20, a novel α‐crystallin isolated from the bovine erythrocyte parasite Babesia bovis, was able to prevent aggregation of denatured alcohol dehydrogenase when the two proteins are present at near equimolar levels. We then examined the ability of Hsp20 produced as two different fusion proteins to prevent Aβ amyloid formation as indicated by Congo Red binding; we found that not only was Hsp20 able to dramatically reduce Congo Red binding, but it was able to do so at molar ratios of Hsp20 to Aβ of 1 to 1000. Electron microscopy confirmed that Hsp20 does prevent Aβ fibril formation. Hsp20 was also able to significantly reduce Aβ toxicity to both SH‐SY5Y and PC12 neuronal cells at similar molar ratios. At high concentrations of Hsp20, the protein no longer displays its aggregation inhibition and toxicity attenuation properties. Size exclusion chromatography indicated that Hsp20 was active at low concentrations in which dimer was present. Loss of activity at high concentrations was associated with the presence of higher oligomers of Hsp20. This work could contribute to the development of a novel aggregation inhibitor for prevention of Aβ toxicity.

Hsp20, a novel alpha-crystallin, prevents Abeta fibril formation and toxicity.

β‐Amyloid (Aβ) is a major protein component of senile plaques in Alzheimers disease, and is neurotoxic when aggregated. The size of aggregated Aβ responsible for the observed neurotoxicity and the mechanism of aggregation are still under investigation; however, prevention of Aβ aggregation still holds promise as a means to reduce Aβ neurotoxicity. In research presented here, we show that Hsp20, a novel α‐crystallin isolated from the bovine erythrocyte parasite Babesia bovis, was able to prevent aggregation of denatured alcohol dehydrogenase when the two proteins are present at near equimolar levels. We then examined the ability of Hsp20 produced as two different fusion proteins to prevent Aβ amyloid formation as indicated by Congo Red binding; we found that not only was Hsp20 able to dramatically reduce Congo Red binding, but it was able to do so at molar ratios of Hsp20 to Aβ of 1 to 1000. Electron microscopy confirmed that Hsp20 does prevent Aβ fibril formation. Hsp20 was also able to significantly reduce Aβ toxicity to both SH‐SY5Y and PC12 neuronal cells at similar molar ratios. At high concentrations of Hsp20, the protein no longer displays its aggregation inhibition and toxicity attenuation properties. Size exclusion chromatography indicated that Hsp20 was active at low concentrations in which dimer was present. Loss of activity at high concentrations was associated with the presence of higher oligomers of Hsp20. This work could contribute to the development of a novel aggregation inhibitor for prevention of Aβ toxicity.

Intracellular gold nanoparticles increase neuronal excitability and aggravate seizure activity in the mouse brain.

Due to their inert property, gold nanoparticles (AuNPs) have drawn considerable attention; their biological application has recently expanded to include nanomedicine and neuroscience. However, the effect of AuNPs on the bioelectrical properties of a single neuron remains unknown. Here we present the effect of AuNPs on a single neuron under physiological and pathological conditions in vitro. AuNPs were intracellularly applied to hippocampal CA1 neurons from the mouse brain. The electrophysiological property of CA1 neurons treated with 5- or 40-nm AuNPs was assessed using the whole-cell patch-clamp technique. Intracellular application of AuNPs increased both the number of action potentials (APs) and input resistance. The threshold and duration of APs and the after hyperpolarization (AHP) were decreased by the intracellular AuNPs. In addition, intracellular AuNPs elicited paroxysmal depolarizing shift-like firing patterns during sustained repetitive firings (SRF) induced by prolonged depolarization (10 sec). Furthermore, low Mg2+-induced epileptiform activity was aggravated by the intracellular AuNPs. In this study, we demonstrated that intracellular AuNPs alter the intrinsic properties of neurons toward increasing their excitability, and may have deleterious effects on neurons under pathological conditions, such as seizure. These results provide some considerable direction on application of AuNPs into central nervous system (CNS).

Zein-based oral drug delivery system targeting activated macrophages.

Reactive oxygen species (ROS) play an important role in the pathogenesis of rheumatoid arthritis (RA). ROS such as hydrogen peroxide and superoxide are overproduced by activated macrophages in RA. As scavengers of ROS, enzymatic proteins such as catalase and superoxide dismutase (SOD) have a great therapeutic potential; however, in vivo application is limited especially when they are orally administered. Although, the oral route is the most convenient for drug administration, therapeutic proteins are easily degraded in vivo by the harsh conditions of gastrointestinal (GI) tract. Here, we introduce a novel drug delivery system composed of zein, a plant storage protein derived from maize. We demonstrate that zein nanoparticles can protect therapeutic proteins, catalase and SOD, from the harsh conditions of GI tract. Folate-conjugated catalase or SOD in zein nanoparticles can target the activated macrophages and scavenge the ROS generated by macrophages in vitro. This novel drug delivery system will be applicable to other orally administered treatments based on the protective property in the harsh conditions of GI tract.

Identifying Common Genetic Risk Factors of Diabetic Neuropathies

Type 2 diabetes mellitus (T2DM) is a global public health problem of epidemic proportions, with 60–70% of affected individuals suffering from associated neurovascular complications that act on multiple organ systems. The most common and clinically significant neuropathies of T2DM include uremic neuropathy, peripheral neuropathy, and cardiac autonomic neuropathy. These conditions seriously impact an individual’s quality of life and significantly increase the risk of morbidity and mortality. Although advances in gene sequencing technologies have identified several genetic variants that may regulate the development and progression of T2DM, little is known about whether or not the variants are involved in disease progression and how these genetic variants are associated with diabetic neuropathy specifically. Significant missing heritability data and complex disease etiologies remain to be explained. This article is the first to provide a review of the genetic risk variants implicated in the diabetic neuropathies and to highlight potential commonalities. We thereby aim to contribute to the creation of a genetic-metabolic model that will help to elucidate the cause of diabetic neuropathies, evaluate a patient’s risk profile, and ultimately facilitate preventative and targeted treatment for the individual.

Zein-alginate based oral drug delivery systems: Protection and release of therapeutic proteins

Reactive oxygen species (ROS) play an important role in the development of inflammatory bowel diseases. Superoxide dismutase (SOD) has a great therapeutic potential by scavenging superoxide that is one of ROS; however, in vivo application is limited especially when it is orally administered. SOD is easily degraded in vivo by the harsh conditions of gastrointestinal tract. Here, we design a zein-alginate based oral drug delivery system that protects SOD from the harsh conditions of gastrointestinal tract and releases it in the environment of the small intestine. SOD is encapsulated in zein-alginate nanoparticles (ZAN) via a phase separation method. We demonstrate that ZAN protect SOD from the harsh conditions of the stomach or small intestine condition. ZAN (200:40) at the weight ratio of 200mg zein to 40mg of alginate releases SOD in a pH dependent manner, and it releases 90.8±1.2% of encapsulated SOD at pH 7.4 in 2h, while only 11.4±0.4% of SOD was released at pH 1.3. The encapsulation efficiency of SOD in ZAN (200:40) was 62.1±2.0%. SOD in ZAN (200:40) reduced the intracellular ROS level and it saved 88.9±7.5% of Caco-2 cells from the toxic superoxide in 4 hours. Based on the results, zein-alginate based oral drug delivery systems will have numerous applications to drugs that are easily degradable in the harsh conditions of gastrointestinal tract.

Association of Diabetes Related Complications with Heart Rate Variability among a Diabetic Population in the UAE.

Microvascular, macrovascular and neurological complications are the key causes of morbidity and mortality among type II diabetes mellitus (T2DM) patients. The aim of this study was to investigate the alterations of cardiac autonomic function of diabetic patients in relation to three types of diabetes-related complications. ECG recordings were collected and analyzed from 169 T2DM patients in supine position who were diagnosed with nephropathy (n = 55), peripheral neuropathy (n = 64) and retinopathy (n = 106) at two hospitals in the UAE. Comparison between combinations of patients with complications and a control diabetic group (CONT) with no complication (n = 34) was performed using time, frequency and multi-lag entropy measures of heart rate variability (HRV). The results show that these measures decreased significantly (p<0.05) depending on the presence and type of diabetic complications. Entropy, (median, 1st- 3rd interquartile range) for the group combining all complications (1.74,1.37–2.09) was significantly lower than the corresponding values for the CONT group (1.77, 1.39–2.24) with lag-1 for sequential beat-to-beat changes. Odds ratios (OR) from the entropy analysis further demonstrated a significantly higher association with the combination of retinopathy and peripheral neuropathy versus CONT (OR: 1.42 at lag 8) and an even OR for the combination of retinopathy and nephropathy (OR: 2.46 at lag 8) compared to the other groups with complications. Also, the OR of low frequency power to high frequency power ratio (LF/HF) showed a higher association with these diabetic-related complications compared to CONT, especially for the patient group combining all complications (OR: 4.92). This study confirms that the type of microvascular or peripheral neuropathy complication present in T2DM patients have different effects on heart rate entropy, implying disorders of multi-organ connectivity are directly associated with autonomic nervous system dysfunction. Clinical practice may benefit from including multi-lag entropy for cardiac rhythm analysis in conjunction with traditional screening methods in patients with diabetic complications to ensure better preventive and treatment outcomes in the Emirati Arab population.

Monocytes: a novel drug delivery system targeting atherosclerosis

Abstract Scavenging of reactive oxygen species (ROS) by antioxidants holds great promise to alleviate the symptoms of cardiovascular diseases and atherosclerosis. In atherosclerosis, damaged endothelial cells (EC) generate more ROS and inflammatory mediators, which recruit more monocytes to the EC. Antioxidants are good therapeutic drug candidates; however, antioxidant enzymes such as catalase are easily degraded by proteases in vivo and chemical mimetics of superoxide dismutase such as tempol and tempo require a target-specific delivery system since hydrophobic tempol or tempo can diffuse into any type of cells non-specifically. Here, we report a novel monocyte-based drug delivery system encapsulating either catalase or tempol/tempo. Monocyte as a novel drug delivery vehicle offers advantages over other delivery systems due to its target specificity to damaged EC. The delivery system can also be easily fabricated in biological conditions and keeps antioxidants active. Membrane impermeable catalase with protease inhibitors was formulated in monocytes via a hypotonic/resealing method and membrane permeable tempol/tempo were encapsulated in monocytes via passive diffusion with 40–60% encapsulation efficiency. Antioxidant-loaded monocytes targeted EC and the antioxidants scavenged more than 90% intracellular ROS generated by cytokines or exogenous ROS. We anticipate numerous applications of the monocyte-based drug delivery system, given its target specificity to activated EC.

Clinical profiles, comorbidities and complications of type 2 diabetes mellitus in patients from United Arab Emirates

Objective To assess clinical profiles of patients with type 2 diabetes in the United Arab Emirates (UAE), including patterns, frequencies, and risk factors of microvascular and macrovascular complications. Research design and methods Four hundred and ninety patients with type 2 diabetes were enrolled from two major hospitals in Abu Dhabi. The presence of microvascular and macrovascular complications was assessed using logistic regression, and demographic, clinical and laboratory data were collected. Significance was set at p<0.05. Results Hypertension (83.40%), obesity (90.49%) and dyslipidemia (93.43%) were common type 2 diabetes comorbidities. Most of the patients had relatively poor glycemic control and presented with multiple complications (83.47% of patients had one or more complication), with frequent renal involvement. The most frequent complication was retinopathy (13.26%). However, the pattern of complications varied based on age, where in patients <65 years, a single pattern presented, usually retinopathy, while multiple complications was typically seen in patients >65 years old. Low estimated glomerular filtration rate in combination with disease duration was the most significant risk factor in the development of a diabetic-associated complication especially for coronary artery disease, whereas age, lipid values and waist circumference were significantly associated with the development of diabetic retinopathy. Conclusions Patients with type 2 diabetes mellitus in the UAE frequently present with comorbidities and complications. Renal disease was found to be the most common comorbidity, while retinopathy was noted as the most common diabetic complication. This emphasizes the need for screening and prevention program toward early, asymptomatic identification of comorbidities and commence treatment, especially for longer disease duration.