METHODOLOGY: A cross-sectional observational study was performed on patients diagnosed with MetS and compared to normal controls. All patients underwent ophthalmic and anthropometric examination, serological and biochemical blood investigations; and ocular imaging using spectral-domain optical coherence tomography. Patients with ocular pathology were excluded. Unpaired t-test was used to compare mean thickness between the two groups. One-way ANOVA with Bonferroni correction for multiple comparisons was used to compare mean thickness between different tertiles of MetS parameters, and a generalized estimating equation was used to correct for inter-eye correlation and to assess association between mean thickness and covariates.
RESULTS: Two hundred and forty-eight eyes from 124 participants (1:1 ratio of MetS patients to controls) were included. Age ranged between 30 to 50 years old, and mean age was 40 ± 6.6 years. RNFL thickness was lower globally (93.6 ± 9.9 μm vs 99.0 ± 9.3, p<0.001) and in the inferior (124.5 ± 17.5 μm vs 131.0 ± 16.4 μm, p = 0.002), superior (117.2 ± 16.0 μm vs 126.3 ± 14.4 μm, p<0.001) and temporal (65.5 ± 10.2 μm vs 69.5 ± 9.8, p = 0.002) sectors in MetS patients compared to controls. Only the central (237.0 ± 14.0 μm vs 243.6 ± 18.0 μm, p = 0.002) and inferior parafoveal (307.8 ± 20.9 vs 314.6 ± 14.6, p = 0.004) area of the macula was significantly thinner. The inferior RNFL sector had the most difference (mean difference = 9.1 μm). The Generalized Estimating Equation found that, after adjusting for age, diastolic blood pressure, BMI, HDL and obesity; the number of MetS components and elevated triglyceride levels were independent risk factors for reduced thickness in global RNFL (β = -4.4, 95% CI = -7.29 to -1.5, p = 0.003) and inferior parafovea (β = -6.85, 95% CI = -11.58 to -2.13, p = 0.004) thickness respectively.
CONCLUSION: RNFL thinning was seen more than macula thinning in MetS patients, suggesting RNFL susceptibility to neurodegeneration than the macula. A higher number of metabolic components and elevated triglyceride levels were independent risk factors for retinal thinning in this group of patients.
MATERIALS AND METHODS: The inhibitory effects of hexane (LHXN), dichloromethane (LDCM), ethyl acetate (LEA) and methanol (LMEOH) extracts from leaves of PS on Aβ-induced production and mRNA expression of pro-inflammatory mediators in BV-2 microglial cells were assessed using colorimetric assay with Griess reagent, ELISA kit and real-time RT-PCR respectively. Subsequently, MTT reduction assay was used to evaluate the neuroprotective effects of PS leaf extracts against Aβ-induced microglia-mediated neurotoxicity in SH-SY5Y neuroblastoma cells. The levels of tau proteins phosphorylated at threonine 231 (pT231) and total tau proteins (T-tau) were determined using ELISA kits.
RESULTS: Polar extracts of PS leaves (LEA and LMEOH) reduced the Aβ-induced secretion of pro-inflammatory cytokines (IL-1β and TNF-α) in BV-2 cells by downregulating the mRNA expressions of pro-inflammatory cytokines. The inhibition of nitric oxide (NO) production could be due to the free radical scavenging activity of the extracts. In addition, conditioned media from Aβ-induced BV-2 cells pre-treated with LEA and LMEOH protected SH-SY5Y cells against microglia-mediated neurotoxicity. Further mechanistic study suggested that the neuroprotective effects were associated with the downregulation of phosphorylated tau proteins.
CONCLUSIONS: The present study suggests that polar extracts of PS leaves confer neuroprotection against Aβ-induced microglia-mediated neurotoxicity in SH-SY5Y cells by attenuating tau hyperphosphorylation through their anti-inflammatory actions and could be a potential therapeutic agent for Alzheimer's disease.