Relationship between amino acid ratios and decline in estimated glomerular filtration rate in diabetic and non-diabetic patients in South Africa.

BACKGROUND: Diabetic kidney disease is a major complication resulting from type 1 and type 2 diabetes. Currently, the microalbuminuria test is used to monitor renal function; however, it does not detect albumin until progressive loss of renal function has occurred. OBJECTIVE: This study analysed the relationship between changes in amino acid ratios and estimated glomerular filtration rate (eGFR) decline in diabetic and non-diabetic patients. METHODS: Urine samples were collected from participants between February 2019 to April 2019 and analysed from November 2020 to January 2021. Diabetic (glycated haemoglobin > 6.4%) and non-diabetic patients (glycated haemoglobin ≤ 6.4%) from Chris Hani Baragwanath Hospital, South Africa, were further categorised based on the degree of renal function predicted by the eGFRs. Amino acids were quantified using tandem mass spectrometry to determine the concentrations and ratios of tyrosine/phenylalanine, ornithine/arginine, arginine/citrulline and citrulline/ornithine at different stages of the chronic kidney disease. RESULTS: Among diabetic patients, the tyrosine/phenylalanine ratio showed a statistically significant increase (p = 0.04) as the eGFR declined from stage 1 to stage 4; the ornithine/arginine ratio showed a strong negative correlation with eGFR. The citrulline/ornithine ratio differed between the diabetic and non-diabetic patients in stage 1 of chronic kidney disease. CONCLUSION: Amino acid ratios (ornithine/arginine and tyrosine/phenylalanine) are affected by the progression of diabetes and can be correlated to renal function. The citrulline/ornithine ratios differ between the studied groups in stage 1 of the disease and may be utilised to predict the onset of chronic kidney disease.

Comparative study of chemical pathology sample collection tubes at the largest hospital in South Africa.

BACKGROUND: BarricorTM Lithium heparin plasma tubes are new blood tubes that have been introduced to overcome the effects of gel in serum separator tubes (SST) and the shortcomings of standard Lithium heparin plasma. We aimed to evaluate BarricorTM tubes as an alternative to serum separator tubes and compare the stability between the tubes. METHODS: Forty-four paired samples were collected using both BarricorTM and SST. We compared five analytes at baseline (<6 h) and after every 24 h using the PassingBablok and Bland-Altman plots. Aspartate aminotransferase (AST), potassium (K), phosphate (PO4) , lactate dehydrogenase (LDH), and creatinine were analysed in both tubes. We calculated the percentage difference for each analyte between the baseline and time intervals to assess analyte stability. The percentage difference was compared to the desirable specification for bias and reference change value (RCV). RESULTS: All analytes were comparable at baseline. Statistical differences (p<0.001) became evident after 24 h. PO4, K, and creatinine had a mean difference that exceeded the desirable specification for bias (-9.59%, - 9.35%, and -4.59%, respectively). Potassium was stable up to 24 h in both tubes. LDH showed better stability in SST (144 h vs 96 h). PO4 concentrations were more stable in both tubes with the SST (96 h vs 72 h). Creatinine and AST had the longest stability in both tubes compared to other analytes (144 h). CONCLUSIONS: Data demonstrated variability and similarities in analyte concentrations and stability, respectively, in both tubes.

Novel APOB missense variants, A224T and V925L, in a black South African woman with marked hypocholesterolemia.

BACKGROUND: One genetic cause of markedly low plasma concentrations of apolipoprotein (apo) B and low density lipoprotein (LDL)-cholesterol is familial hypobetalipoproteinemia. OBJECTIVE: We aimed to determine the molecular basis for the marked hypocholesterolemia consistent with heterozygous familial hypobetalipoproteinemia in a black female subject of Xhosa lineage. METHODS: Coding regions of APOB, MTTP, PCSK9,ANGPTL3, SAR1B and APOC3 were sequenced, and APOE was genotyped. COS-7 cells were transfected with plasmids containing apoB variants. Western blotting was used to detect cellular and secreted apoB, and co-immunoprecipitation performed to assess binding with the microsomal triglyceride transfer protein (MTP). RESULTS: Sequence analysis of the APOB gene revealed her to be heterozygous for two novel variants, c.751G>A (A224T) and c.2854G>C (V925L). She was also homozygous for the APOEε2 allele, and did not carry a PCSK9 loss-of-function mutation. Although Ala(224) is within the postulated MTP binding region in apoB, it is not conserved among mammalian species. Subsequent genotyping showed that Ala224Thr is found in a southern African population (n=654) with an allele frequency of 1.15% and is not associated with plasma lipid levels. Val(925), like Ala(224), is within the N-terminal 1000 amino acids required for lipoprotein assembly, but was not found in the population screen. However, in vitro studies showed that apoB V925L did not affect apoB48 production or secretion nor have a deleterious effect on MTP interaction with apoB. CONCLUSION: Taken together, this suggests that the hypocholesterolemia in our case may be a result of being homozygous for APOEε2 with a low baseline cholesterol.

The C679X mutation in PCSK9 is present and lowers blood cholesterol in a Southern African population.

OBJECTIVE: Missense mutations in the proprotein convertase subtilisin/kexin type 9 gene (PCSK9) can cause familial hypercholesterolemia. However, two nonsense variants of PCSK9, Y142X and C679X, found in approximately 2% of black American subjects, are associated with a 28% reduction in mean low density lipoprotein (LDL)-cholesterol. We sought to determine the frequency and effect of these nonsense variants in an African population. METHODS AND RESULTS: PCSK9 genotypes were determined in 653 black African women attending two antenatal clinics in Zimbabwe. C679X occurred in 3.7% of subjects and was associated with a 27% reduction in LDL-cholesterol (1.6+/-0.3 mmol/L versus 2.2+/-0.7 mmol/L in non-carriers). We did not observe the Y142X variant. CONCLUSIONS: Our results show that the PCSK9 C679X variant has a marked cholesterol-lowering effect.