RRM2 attenuates the renal tubular ferroptosis in diabetic kidney disease through PI3K/Akt/Nrf2 pathway

Table 1 Baseline characteristics of the study population

Characteristics	Control (n = 120)	T2DM (n = 194)	P value
Age (years)	56.80 ± 10.41	55.16 ± 9.67	0.158
Sex (male), n (%)	68 (56.7)	101 (52.1)	0.426
BMI (kg/m2)	24.01 ± 1.24	24.55 ± 1.15	< 0.001
Duration (years)	0	9.14 ± 2.01	< 0.001
SBP (mmHg)	123.44 ± 11.21	136.82 ± 15.18	< 0.001
FBG (mmol/L)	4.72 ± 0.66	7.76 ± 1.15	< 0.001
HbA1c (%)	4.98 ± 0.82	7.94 ± 1.17	< 0.001
TG (mmol/L)	1.89 ± 0.79	2.11 ± 0.82	0.021
TC (mmol/L)	5.29 ± 0.47	5.50 ± 0.72	0.002
eGFR (mL/minute/1.73 m2)	105.24 ± 18.35	99.47 ± 22.12	0.017
Scr (μmol/L)	67.92 ± 10.40	82.56 ± 17.46	< 0.001
Urinary NGAL (ng/mL)	6.57 ± 0.92	8.62 ± 1.51	< 0.001
Urinary KIM-1 (ng/mL)	1.01 ± 0.24	1.30 ± 0.36	< 0.001
MDA (nmol/mL)	7.30 ± 1.13	9.14 ± 1.51	< 0.001
GSH (nmol/mL)	10.76 ± 1.75	8.31 ± 1.92	< 0.001
SLC7A11 (pg/mL)	141.36 ± 16.28	125.04 ± 19.26	< 0.001
GPX4 (ng/mL)	175.23 ± 23.89	139.14 ± 20.87	< 0.001
RRM2 (pg/mL)	24.17 ± 3.83	37.39 ± 6.69	< 0.001

Continuous variables are expressed as mean ± SD, and analyzed using t-test or Wilcoxon-Mann-Whitney test. Categorical variables are expressed as frequency (percentage), and analyzed using the χ² test. T2DM: Type 2 diabetes mellitus; BMI: Body mass index; SBP: Systolic blood pressure; FBG: Fasting blood glucose; HbA1c: Glycosylated hemoglobin; TG: Triglyceride; TC: Total cholesterol; eGFR: Estimated glomerular filtration rate; Scr: Serum creatinine; NGAL: Neutrophil gelatinase-associated lipocalin; KIM-1: Kidney injury molecule-1; MDA: Malondialdehyde; GSH: Glutathione; SLC7A11: Solute carrier family 7 member 11; GPX4: Glutathione peroxidase 4; RRM2: Ribonucleotide reductase regulatory subunit M2.

Table 2 Baseline characteristics between all subgroups of type 2 diabetes mellitus

Characteristics	Normoalbuminuria (n = 93)	Microalbuminuria (n = 58)	Macroalbuminuria (n = 43)	P value
Age (years)	52.93 ± 9.33	55.93 ± 9.87	58.98 ± 8.96	0.002
Sex (male), n (%)	46 (49.5)	31 (53.4)	24 (55.8)	0.764
BMI (kg/m2)	24.23 ± 1.03	24.74 ± 1.18	24.98 ± 1.18	0.001
Duration (years)	8.03 ± 1.37	9.54 ± 1.67	10.99 ± 2.05	< 0.001
SBP (mmHg)	130.61 ± 13.72	140.40 ± 13.10	145.44 ± 15.32	< 0.001
FBG (mmol/L)	7.50 ± 1.01	7.82 ± 0.93	8.25 ± 1.49	0.001
HbA1c (%)	7.74 ± 0.93	8.02 ± 1.42	8.23 ± 1.21	0.065
TG (mmol/L)	1.97 ± 0.79	2.21 ± 0.88	2.28 ± 0.78	0.061
TC (mmol/L)	5.34 ± 0.70	5.57 ± 0.74	5.75 ± 0.66	0.006
eGFR (mL/min/1.73 m2)	110.87 ± 22.75	97.40 ± 12.07	77.60 ± 11.53	< 0.001
Scr (μmol/L)	72.07 ± 9.14	82.92 ± 12.70	104.77 ± 15.79	< 0.001
Urinary NGAL (ng/mL)	8.17 ± 1.31	8.72 ± 1.56	9.46 ± 1.51	< 0.001
Urinary KIM-1 (ng/mL)	1.21 ± 0.32	1.34 ± 0.32	1.43 ± 0.42	0.002
MDA (nmol/mL)	8.50 ± 1.13	9.27 ± 1.47	10.35 ± 1.54	< 0.001
GSH (nmol/mL)	9.37 ± 1.66	7.79 ± 1.54	6.73 ± 1.50	< 0.001
SLC7A11 (pg/mL)	135.23 ± 16.74	121.14 ± 15.64	108.24 ± 14.79	< 0.001
GPX4 (ng/mL)	150.92 ± 17.42	135.91 ± 15.77	118.04 ± 14.88	< 0.001
RRM2 (pg/mL)	40.51 ± 6.32	36.29 ± 5.59	32.12 ± 4.91	< 0.001

BMI: Body mass index; SBP: Systolic blood pressure; FBG: Fasting blood glucose; HbA1c: Glycosylated hemoglobin; TG: Triglyceride; TC: Total cholesterol; eGFR: Estimated glomerular filtration rate; Scr: Serum creatinine; NGAL: Neutrophil gelatinase-associated lipocalin; KIM-1: Kidney injury molecule-1; MDA: Malondialdehyde; GSH: Glutathione; SLC7A11: Solute carrier family 7 member 11; GPX4: Glutathione peroxidase 4; RRM2: Ribonucleotide reductase regulatory subunit M2.

Table 3 Correlation between serum ribonucleotide reductase regulatory subunit M2 and clinical indicators

Parameters	All subjects (n = 194)
	r value	P value
Age (years)	-0.147	0.041
BMI (kg/m2)	-0.126	0.080
Duration (years)	-0.390	< 0.001
SBP (mmHg)	-0.210	0.003
FBG (mmol/L)	-0.223	0.002
HbA1c (%)	-0.156	0.030
TG (mmol/L)	-0.022	0.763
TC (mmol/L)	-0.027	0.705
eGFR (mL/min/1.73 m2)	0.263	< 0.001
Scr (μmol/L)	-0.315	< 0.001
Urinary NGAL (ng/mL)	-0.153	0.034
Urinary KIM-1 (ng/mL)	-0.234	0.001
MDA (nmol/mL)	-0.326	< 0.001
GSH (nmol/mL)	0.275	< 0.001
SLC7A11 (pg/mL)	0.269	< 0.001
GPX4 (ng/mL)	0.305	< 0.001

The correlation between serum ribonucleotide reductase regulatory subunit M2 and other continuous variables, and was analyzed using the Pearson correlation test. BMI: Body mass index; SBP: Systolic blood pressure; FBG: Fasting blood glucose; HbA1c: Glycosylated hemoglobin; TG: Triglyceride; TC: Total cholesterol; eGFR: Estimated glomerular filtration rate; Scr: Serum creatinine; NGAL: Neutrophil gelatinase-associated lipocalin; KIM-1: Kidney injury molecule-1; MDA: Malondialdehyde; GSH: Glutathione; SLC7A11: Solute carrier family 7 member 11; GPX4: Glutathione peroxidase 4; RRM2: Ribonucleotide reductase regulatory subunit M2.

Table 4 Logistic multivariate regression for developing diabetic nephropathy

Characteristics	Odds ratio	95% confidence interval	P value
Duration (years)	1.854	1.191-2.884	0.006
SBP (mmHg)	1.091	1.026-1.160	0.005
eGFR (mL/min/1.73 m2)	0.946	0.909-0.986	0.008
Scr (μmol/L)	1.136	1.058-1.219	< 0.001
GSH (nmol/mL)	0.438	0.272-0.703	0.001
SLC7A11 (pg/mL)	0.953	0.911-0.998	0.041
GPX4 (ng/mL)	0.925	0.885-0.966	< 0.001
RRM2 (pg/mL)	0.820	0.712-0.945	0.006

SBP: Systolic blood pressure; eGFR: Estimated glomerular filtration rate; Scr: Serum creatinine; GSH: Glutathione; SLC7A11: Solute carrier family 7 member 11; GPX4: Glutathione peroxidase 4; RRM2: Ribonucleotide reductase regulatory subunit M2.