Lipoprotein(a) as an independent risk factor for diabetic retinopathy in male patients in non-insulin-dependent diabetes mellitus

Lipoprotein (a) as a predictor of diabetic retinopathy in patients with type 2 diabetes: A systematic review

BACKGROUND

Lipoprotein a (LP(a)), an LDL-like lipoprotein, known as a risk factor for cardiovascular diseases, has a controversial association with diabetic retinopathy in patients with type 2 diabetes-the current systematic review aimed to critically assess the association between LP(a) and diabetic retinopathy.

METHODS

A systematic review of relevant studies was conducted after a thorough search in PubMed, Scopus, and Google Scholar electronic databases. We used English observational, case-control, and prospective cohort studies published up to August 2022, including type 2 diabetic patients as the population, diabetic retinopathy as the outcome, and LP(a) as the intervention.

RESULT

17 relevant studies, including 4688 patients with diabetes, were included in this systematic review. While in 13 studies, Lipoprotein(a) was recognized as a risk factor for diabetic retinopathy, only three studies reported no evidence of a relationship between the two. Also, another study showed a mixed outcome of the relationship between LP(a) and diabetic retinopathy.

CONCLUSION

High serum lipoprotein(a) in patients with type 2 diabetes is considered a risk factor for diabetic retinopathy. However, further large-scaled cohort studies are still required to validate this finding.

The role of lipids in the development of diabetic microvascular complications: implications for therapy

Dyslipidemia is a major factor responsible for coronary heart disease and its reduction decreases coronary risk in patients with diabetes mellitus. However, the association of dyslipidemia with microvascular complications and the effect of intervention with lipid-lowering therapy in diabetes have been less investigated. We present the systematic review of association and intervention studies pertaining to dyslipidemia and microvascular disease in diabetes and also review possible mechanisms. Dyslipidemia may cause or exacerbate diabetic retinopathy and nephropathy by alterations in the coagulation-fibrinolytic system, changes in membrane permeability, damage to endothelial cells and increased atherosclerosis. Hyperlipidemia is associated with faster decline in glomerular filtration rate and progression of albuminuria and nephropathy. Recent evidence also suggests a role of lipoprotein(a) in progression of retinopathy and nephropathy in patients with diabetes mellitus. Lipid-lowering therapy, using single agents or a combination of drugs may significantly benefit diabetic retinopathy and diabetic nephropathy. In particular, hydroxymethyl glutaryl coenzyme A reductase inhibitors may be effective in preventing or retarding the progression of microvascular complications because of their powerful lipid-lowering effects and other additional mechanisms. However, most of the data are based on short-term studies, and need to be ascertained in long-term studies. Until more specific guidelines are available, aggressive management of diabetic dyslipidemia, according to currently accepted guidelines, should be continued for the prevention of macrovascular disease which would also benefit microvascular complications.

Relation of apolipoprotein (a) phenotypes to diabetic retinopathy in elderly type 2 diabetes

The aim of this study was to clarify the relationship between apolipoprotein (a) (apo (a) ) phenotypes and diabetic retinopathy in elderly type 2 diabetes. Serum Lp (a) concentrations and apo (a) phenotypes were analyzed in 250 diabetic patients aged 60 to 88 years old. Apo (a) phenotypes were classified into 7 subtypes (F, B, S1, S2, S3, S4, O (Null) ) by the method SDS electrophoresis with Western blotting. Patients were divided into two groups according to their apo (a) phenotypes:a low molecular weight (LMW) Lp (a) group, and a high molecular weight (HML) Lp (a) group. Patients were classified as having one of 4 types of diabetic retinopathy: no retinopathy (R0), simple retinopathy (R1), pre-proliferative retinopathy (R2), and proliferative retinopathy (R3). There was a significant association between serum Lp (a) levels and severity of diabetic retinopathy (p<0.001). A gradual trend toward increasing serum Lp (a) levels was observed across the groups (from R0 to R3). A significantly greater percentage of LMW Lp (a) was observed in the R1, R2, and R3 groups than in the R0 group (42.9% (p<0.001), 27.0% (p<0.01), and 27.3% (p<0.05) vs. 10.4%). Multiple logistic regression analysis revealed that duration of diabetes and LMW Lp (a) are independent risk factors for diabetic retinopathy. These results provide significant evidence that LMW Lp (a) contributes to an increased risk of diabetic retinopathy in elderly type 2 diabetes.

Comparison of risk factors of macrovascular complications. Peripheral vascular disease, cerebral vascular disease, and coronary heart disease in Japanese type 2 diabetes mellitus patients

Although macroangiopathies such as peripheral vascular disease (PVD), cerebral vascular disease (CVD), and coronary heart disease (CHD) can often be observed in patients with diabetes mellitus, they are not specific for diabetes mellitus. Moreover, it is unclear whether their progressive mechanism is different. In the present study, we compared the risk factors among the diabetic macrovascular complications. Univariate analyses showed that in all patients, age at examination, duration of diabetes, thrombin-antithrombin III complex (TAT) level, fibrinogen level, lipoprotein (a) (Lp(a)) level, total cholesterol (T-Chol) level, and existence of microagiopathy were risk factors for PVD. Age, duration of diabetes, insulin level, TAT level, fibrinogen level, HDL cholesterol (HDL-Chol) level, hypertension, and nephropathy were risk factors for CVD. Only fibrinogen level was a risk factor for CHD. Moreover, Lp(a) level was a risk factor for PVD and CVD in male patients, but not in females. On the other hand, insulin level was a risk factor for CVD in female patients, but not in males. Multivariate analyses showed that TAT level, T-Chol level, and neuropathy were independent variables for PVD and that age, TAT level, and HDL-Chol level were independent variables for CVD. On the other hand, only fibrinogen level was the independent variable for CHD in males. Our results suggest that the progressive mechanism of PVD and CVD might be different from that of CHD and might differ according to gender in Japanese diabetic patients.