rs316019 — SLC22A2 Ala270Ser

Reduces OCT2 organic cation transporter function in the kidney, lowering metformin renal clearance and conferring partial protection against cisplatin ototoxicity and nephrotoxicity

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SLC22A2 encodes organic cation transporter 2 (OCT2), the dominant transporter on the basolateral membrane of kidney proximal tubule cells. OCT2 is responsible for the first and rate-limiting step in renal secretion of metformin: uptake from the bloodstream into tubular epithelial cells. Without efficient OCT2 transport, metformin accumulates in plasma at higher concentrations than expected — which may enhance glucose lowering but also risks lactic acidosis in susceptible patients. The same transporter also mediates uptake of cisplatin and oxaliplatin into renal and cochlear cells, making OCT2 genotype a determinant of platinum chemotherapy toxicity.

OCT2 operates as an electrogenic uniporter driven by the inside-negative membrane potential of proximal tubule cells.

Reduced OCT2 function has a dual consequence for platinum drugs: in cochlear hair cells and renal tubular cells, cisplatin entry depends on OCT2. Carriers with reduced OCT2 activity take up less cisplatin into these sensitive tissues, partially protecting against hearing loss and kidney injury.

Metformin pharmacokinetics:

A clinical pharmacokinetic study of healthy subjects demonstrated that rs316019 carriers had significantly lower metformin renal clearance compared to non-carriers, with correspondingly higher Cmax and AUC. The same pattern was reported in a Korean healthy volunteer study, where subjects with the c.808G>T variant showed higher metformin Cmax and altered AUC compared to wild-type GG carriers .

A mechanistic study found that SLC22A2 c.596C>T, c.602C>T, and c.808G>T all showed significant differences in metformin pharmacokinetics11 all showed significant differences in metformin pharmacokinetics
Song et al. Clin Pharmacol Ther 2008 compared to the reference genotype, with decreased transporter function resulting in reduced renal metformin clearance and consequently increased plasma concentrations.

A critical caveat comes from a controlled interaction study: when rs316019 was analyzed in isolation without co-consideration of MATE1 variants, the effect on metformin clearance was not statistically significant. Only when examining the combined genotype with MATE1 rs2252281 did the OCT2 variant produce significant changes in renal clearance (28.1 to 44.8 L/h, p=0.004)22 renal clearance (28.1 to 44.8 L/h, p=0.004)
Christensen et al. Pharmacogenet Genomics 2013, n=50 healthy Caucasians.

Cisplatin toxicity:

In 130 patients (64 pediatric, 66 adult) receiving cisplatin-based chemotherapy, the rs316019 GT heterozygous genotype conferred striking protection against cisplatin-induced ototoxicity33 cisplatin-induced ototoxicity
Lanvers-Kaminsky et al. Pharmacogenomics 2015 with OR 0.12 (95% CI 0.02–0.67, p=0.009) — an 88% relative risk reduction for hearing damage versus GG homozygotes.

In a Chinese cohort of 123 cancer patients, the GT/TT genotype was also associated with smaller increases in cystatin C (a sensitive marker of kidney damage) following cisplatin treatment compared to GG carriers (P=0.043). Paradoxically, a separate study reported that rs316019 carriers had higher baseline urinary KIM-1 (kidney injury molecule-1) levels, and elevated KIM-1 at day 3 and day 10 post-cisplatin, suggesting that the relationship between OCT2 genotype and cisplatin nephrotoxicity is more complex than simple protection.

For metformin users: The standalone pharmacokinetic effect of rs316019 is modest. Heterozygotes and homozygotes may accumulate slightly higher plasma metformin levels, which becomes clinically relevant mainly in situations of renal impairment, dehydration, iodinated contrast administration, or concurrent use of OCT2 inhibitors such as cimetidine, ranitidine, or trimethoprim.

For oncology patients: If you carry the rs316019 A allele and are scheduled to receive cisplatin-based chemotherapy, this information may be valuable for your oncologist. The reduced cisplatin uptake into cochlear hair cells appears to lower ototoxicity risk, which is particularly relevant in pediatric oncology where hearing preservation is critical for development. This finding should be weighed against the potential for altered cisplatin efficacy.

OCT2 interacts with OCT1 (SLC22A1, rs622342) in determining overall metformin handling: OCT1 controls hepatic uptake (determining the glucose-lowering effect), while OCT2 controls renal secretion (determining drug clearance and plasma levels). Combined OCT1+OCT2 poor transporter status would create a complex pharmacokinetic picture: reduced hepatic efficacy and reduced renal clearance simultaneously.

Drug Interactions

metformin dose_adjustment literature
cisplatin reduced_efficacy literature
oxaliplatin dose_adjustment literature

Genotype Interpretations

What each possible genotype means for this variant.

CC Normal OCT2 Function Normal

Standard OCT2 transporter activity — typical metformin renal clearance

You have two copies of the common C allele at rs316019. Your OCT2 transporter functions at full capacity, efficiently secreting metformin and other organic cations from blood into urine through the kidney proximal tubule. This is the most common genotype, found in approximately 80% of people across ancestries. Standard metformin pharmacokinetics apply, and your renal clearance of OCT2-transported drugs follows expected patterns.

AC Intermediate OCT2 Function Intermediate

One reduced-function allele — moderately decreased metformin renal clearance

The heterozygous state means roughly half of your OCT2 protein at the proximal tubule basolateral membrane is normal and half is the reduced-function variant. In isolation, the impact on metformin clearance is modest and may not produce obvious clinical effects at standard doses in patients with normal renal function. However, any additional factor that stresses renal OCT2 capacity — impaired kidney function, dehydration, iodinated contrast media, or OCT2-inhibiting drugs like cimetidine, ranitidine, or trimethoprim — can unmask the reduced clearance and lead to metformin accumulation.

AA Reduced OCT2 Function Reduced

Two reduced-function alleles — substantially decreased metformin renal clearance

With both OCT2 alleles encoding the reduced-function variant, your kidney's capacity to actively secrete metformin is substantially diminished. The magnitude of the effect is clinically significant: renal clearance may be reduced compared to CC homozygotes. At standard metformin doses (1500–2000 mg daily), plasma metformin levels are higher than in CC carriers, increasing the theoretical risk of lactic acidosis — a rare but serious complication (mortality 30–50% when it occurs) that is strongly associated with renal metformin accumulation. OCT2 inhibitors (cimetidine, ranitidine, trimethoprim, dolutegravir) are particularly dangerous to combine with metformin in this genotype.