Association of tumor necrosis factor-alpha -308 G/A and -238 G/A polymorphism with diabetic retinopathy: a systematic review and updated meta-analysis

Elevated aqueous TNF-α levels are associated with more severe functional and anatomic findings in eyes with diabetic macular oedema

BACKGROUND

Intravitreal ranibizumab for diabetic macular oedema (DMO) has been recently shown to modulate levels of aqueous cytokines. This study investigates the associations between changes in aqueous cytokine levels following intravitreal ranibizumab therapy and the corresponding anatomical and functional changes in the eye.

METHODS

Twenty-five patients comprising 30 eyes diagnosed with DMO were prospectively recruited. All eyes received three loading dose ranibizumab injections at baseline, week 4 and week 8, followed by pro re nata treatment based on best-corrected visual acuity (BCVA) and central macular thickness (CMT) up to week 48. Prior to ranibizumab administration, aqueous samples were collected from all eyes, and subsequent sampling was performed at week 8. Levels of 32 cytokines were assessed at baseline and at week 8.

RESULTS

At baseline, higher aqueous TNF-α levels were associated with poorer BCVA (p = 0.033), greater macular volume (p = 0.017) and worse diabetic retinopathy (p = 0.047). Higher levels of IL-7 were associated with poorer BCVA and greater macular volume (MV). Following treatment with ranibizumab there was a significant correlation with reduction of aqueous TNF-α and improvements in BCVA and MV, both at 6 months (BCVA [r = -0.558, p = 0.001], MV [r = 0.410, p = 0.024]) and 12-months (BCVA [r = -0.413, p = 0.023], MV [r = 0.482, p = 0.008]). The change in VEGF concentration following ranibizumab treatment did not correlate with either BCVA or MV improvements (p > 0.05).

CONCLUSIONS

Higher levels of aqueous TNF-α and IL-7 correlated with worse DMO, both anatomically and functionally. Reductions in levels of aqueous TNF-α, but not VEGF, post ranibizumab treatment were associated with improvement in BCVA and MV.

Is TNF alpha a mediator in the co-existence of malaria and type 2 diabetes in a malaria endemic population?

Malaria remains a disease of public health importance globally, especially in sub-Saharan Africa. Malaria deaths reduced globally steadily between 2000-2019, however there was a 10% increase in 2020 due to disruptions in medical service during the COVID-19 pandemic. Globally, about 96% of malaria deaths occurred in 29 countries; out of which, four countries (Nigeria, the Democratic Republic of the Congo, the Niger, and the United Republic of Tanzania) accounted for just over half of the malaria deaths. Nigeria leads the four countries with the highest malaria deaths (accounting for 31% globally). Parallelly, sub-Saharan Africa is faced with a rise in the incidence of Type 2 diabetes (T2D). Until recently, T2D was a disease of adulthood and old age. However, this is changing as T2D in children and adolescents is becoming an increasingly important public health problem. Nigeria has been reported to have the highest burden of diabetes in Africa with a prevalence of 5.77% in the country. Several studies conducted in the last decade investigating the interaction between malaria and T2D in developing countries have led to the emergence of the intra-uterine hypothesis. The hypothesis has arisen as a possible explanation for the rise of T2D in malaria endemic areas; malaria in pregnancy could lead to intra-uterine stress which could contribute to low birth weight and may be a potential cause of T2D later in life. Hence, previous, and continuous exposure to malaria infection leads to a higher risk of T2D. Current and emerging evidence suggests that an inflammation-mediated link exists between malaria and eventual T2D emergence. The inflammatory process thus, is an important link for the co-existence of malaria and T2D because these two diseases are inflammatory-related. A key feature of T2D is systemic inflammation, characterized by the upregulation of inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) which leads to impaired insulin signaling. Malaria infection is an inflammatory disease in which TNF-α also plays a major role. TNF-α plays an important role in the pathogenesis and development of malaria and T2D. We therefore hypothesize that TNF-α is an important link in the increasing co-existence of T2D.

The Role of Adaptive Immunity in Diabetic Retinopathy

Diabetic retinopathy (DR) is currently one of the common causes of vision loss in working-age adults. It is clinically diagnosed and classified according to the vascular changes in the fundus. However, the activation of immune cells occurs before these vascular changes become detectable. These, together with molecular studies and the positive clinical outcomes of anti-inflammatory treatment, highlight the pivotal involvement of the immune system. The role of innate immunity in DR pathophysiology has been studied in depth, but the contribution of adaptive immunity remains largely elusive. This review aims to summarize our current understanding of the activation mechanism of adaptive immunity in DR microenvironments and to discuss the relationship between adaptive immunity and local vascular units or innate immunity, which opens new avenues for clinical applications in DR treatment.